Electrical discharge devices and techniques for medical procedures

ABSTRACT

A medical instrument coupled to first and second energy means and a computer controller for the controlled volumetric removal of thin tissue layers. The system provides a source for introducing a gas to controllably form and capture transient gas volumes in a microchannel structure at the working surface of the instrument that interfaces with a targeted tissue site. Each of the microchannel features of the working surface carries an electrode element coupled to the electrical source. The energy may be applied to the targeted site in either of two modes of operation, depending in part on voltage and repetition rate of energy delivery. In one mode of energy application, electrical potential is selected to cause an intense electrical arc across the transient ionized gas volumes to cause an energy-tissue interaction characterized by tissue vaporization. In another preferred mode of energy delivery, the system applies selected levels of energy to the targeted site by means of an energetic plasma at the instrument working surface to cause molecular volatilization of surface macromolecules thus resulting in material removal. Both modes of operation limit collateral thermal damage to tissue volumes adjacent to the targeted site. Another preferred embodiment provides and an ultrasound source or other vibrational source coupled to the working end to cause cavitation in fluid about the working end.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/065,180 (Attorney Docket No. 022356-000310US), filed Feb. 23, 2005,which was a continuation of Ser. No. 10/282,555 (Attorney Docket No.022356-000300US), filed Oct. 28, 2002, which was a continuation-in-partof U.S. patent application Ser. No. 09/614,163, filed Jul. 11, 2000,titled Electrical Discharge Devices and Techniques for Plasma-AssistedSkin Resurfacing, which was a continuation-in-part of U.S. patentapplication Ser. No. 09/317,768, filed May 24, 1999, titled PhotoionizedGas Enabled Electrical Discharge Technique for Plasma-Mediated ColdTissue Ablation, the full disclosures which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to electrosurgical instruments and techniquesfor precision application of energy to tissue, and more particularly toa system for thin layer ablation. More in particular, the workingsurface of a probe carries (i) delivery means for introducing andcapturing a gas volume in a microchannel structure at an interfacebetween the probe and the targeted site, (ii) energy delivery means forcreating an intense electrical field of micron-dimensioned gas volumesto controllably apply intense energy to the targeted site to causevolumetric tissue removal, and (iii) vibration means for assisting inthe creation of micron-scale gas volumes or bubbles.

2. Description of the Background Art

Various electromagnetic and acoustic energy delivery sources have beeninvestigated for surgical tissue ablation or removal, includingradiofrequency (Rf) current flow within tissue, high intensity focusedultrasound (HFU) tissue interactions and microwave energy absorption intissue. In general, at high intensities, the above listed energy sourcesgenerate thermal effects that can vaporize tissue as the means of tissueablation or removal. In other words, the energy sources elevate thetemperature of water in intra- and extracellular spaces to above 100° C.thereby explosively vaporizing water to damage or destroy the tissue.The drawback to such purely thermally-mediated ablations is significantcollateral damage to tissue volumes adjacent to the targeted site. Whilein many surgical fields, the above-described collateral thermal damagemay be acceptable, in fields such where thin layer ablations arerequired, such as skin resurfacing, ophthalmology, neurology, andinterventional cardiology, there is a need to prevent, or limit, anysuch collateral damage.

Lasers for Use in Tissue Ablation. Various laser systems have beendeveloped for tissue ablation. The conventional long-pulse laser systemsoutside the UV range, wherein long-pulse is defined as a systemoperating in a range of 10's of nanoseconds to microseconds in pulseduration, have been found to be inefficient in volumetric tissue removalwithout causing extensive collateral damage. In a the conventionallong-pulse laser system (e.g., Nd:YAG, Er:YAG, IR lasers), the photonicenergy delivered to a targeted site does not directly disrupt themolecular integrity of surface layers of the site, but rather the energyis transferred into surrounding tissue volumes as photothermal energy,or photomechanical energy. These collateral effects propagate throughsurrounding tissues as heat, and perhaps mechanical shock waves, whichmanifest themselves as undesirable collateral damage. More specifically,the generally accepted model of volumetric ablation or removal withlasers having a pulse longer than tens or hundreds of picoseconds isdescribed as follows: The energy absorption is chromophore dependent(and/or scattering dependent), and the energy transfer involves theheating of conduction band electrons by the incident beam of coherentphotons which is followed by transfer of thermal energy to thestructure's lattice. Ablation or damage occurs by conventional heatdeposition resulting in vaporization, melting, or fracture of thestructure. The rate of volumetric structure removal depends on thermalconduction through the structure lattice and its thermodynamicproperties (heat capacity, heat of vaporization, heat of fusion, etc.).Thus, the minimum energy requirements to cause an ablation effect in thestructure's properties may be defined by a threshold of incident laserenergy per unit of structure volume at the target site, which thresholdis directly dependent on pulse duration. It has been found that ablationthresholds generally require relatively long pulse durations, which inturn are the source of undesirable collateral photothermal (orphotomechanical) damage.

In certain tissue ablation fields (e.g., corneal ablation inophthalmology), excimer lasers have been developed that emit highintensity pulses of ultraviolet (UV) light, typically with pulsedurations in the 1 ns to 100 ns range. The short wavelengths, as well assequenced nanosecond pulse regimes, define a substantially non-thermallymediated form of tissue ablation. Short wavelength UV photons are highlyenergetic and when radiated onto biological tissue can directly breakthe chemical bonds in surface layer molecules of the tissue. As aconsequence, UV excimer lasers can vaporize or breakdown a surfacetissue layer with minimal thermal energy transfer to underlying (oradjacent) tissue volumes. The by-product of the breakdown ispredominantly a gas that is ejected away from the surface on which theenergy was deposited, thus generally leaving the subsurface layer freefrom substantial collateral thermal damage. Tissue ablation with UVirradiation with can be controlled depth-wise since biological tissuesexhibit strong absorption in the UV region of the electromagneticspectrum (e.g., at c. 1.93 μm). In biological tissue, UV radiationtypically only penetrates to a depth of from about 0.25 μm to about 4.0μm per pulse in the ns duration pulses described above. Thus, to ablateto a certain depth, the system uses a pre-determined number of pulses ofns energy delivery

While UV photonic energy delivery can reduce collateral damage in tissueablation, there are numerous disadvantages that limit the applicabilityof UV lasers to biomedical procedures. First, UV photonic energydelivery cannot be easily delivered to a targeted site of a bodystructure in a fluid environment (e.g., thrombus in a blood vessel)since intervening fluid may absorb energy rather than the target site.For this reason, UV energy delivery is most useful for ablating tissuesurfaces exposed to the atmosphere, such as a patient's cornea in aLASIK procedure. Second, the desired lack of collateral damage in UVablation is known to occur when a single pulse of UV photonic energyirradiates a tissue surface. However, when the UV pulse repetition rateexceeds about 5 to 10 Hz, considerable photothermal collateral damage(as well as photomechanical collateral damage) has been observed. Thus,UV ablation generally may result in low volumetric removals of tissuesurfaces per unit of time. Third, while UV photons carry sufficientenergy to directly break chemical bonds in surface molecules of tissue,UV wavelengths also may be sufficiently energetic to promote mutageniceffects thus elevating concerns about the long-term health and health ofthe clinician and the patient.

Conventional Electrosurgical Ablation of Tissue Volumes. Radiofrequencycurrents in tissue have been known for many years in the prior art forcutting a tissue mass, or for coagulating regions within a tissue mass.Conventional electrosurgical systems known in the art ablate tissue byapplying an electrical field across the tissue to be treated. The actualenergy-tissue interaction in Rf cutting is typically described in termsof a voltage differential that causes a spark or arc across a gapbetween an active electrode 2 a and the targeted site (e.g., coupled toa return electrode 2 b) as shown in FIG. 1A. In the prior art instrumentof FIG. 1A, a high energy density capable of tissue cutting is createdwhen the gap between the active electrode 2 a and the tissue surface isoccupied with an electrically non-conductive gas, or an electricallyinsulative liquid. FIG. 1A depicts a typical ablation modality in whichelectrode 2 a is moved into contact with a liquid or moisture layer onan exposed tissue mass which vaporizes a plurality of random bubbles 3.The bubbles comprise insulative gas volumes and randomly can form amomentary insulative physical gap between the active electrode 2 a andthe tissue (coupled to return electrode 2 b) resulting in a spark acrossthe gap. Such an Rf spark created between the active electrode and thetissue will cause localized damage and ablation at the dischargeconduction site at the surface of the tissue. In other words, the sparkcauses very high energy densities at the random location that the tissueinterfaces the bubble 3 which in turn results in intense heat thatdisrupts and ablates a site on the tissue surface. In FIG. 1A, it can beseen that conductive paths 4 indicate the paths of current flow. Theconventional electrosurgical ablation of FIG. 1A generally is achievedat frequencies ranging from 500 kHz to 2.5 MHz, with power levelsranging from 75 to 750 W. In such prior art tissue cutting with Rfcurrents, the current density rapidly decreases with distance from theexact energy deposition site on the tissue which is contacted by thespark. Still, the depth of tissue disruption and damage in such priorart electrosurgical cutting may range from about 0.3 mm. to as much as3.5 mm. (see R. D. Tucker et al, Histologic characteristics ofelectrosurgical injuries, Journal Am. Assoc. Gynecol. Laparoscopy 4(2),pp. 201-206 1997.) The depth of tissue ablation depends on severalvariables, including (i) the conductivity of the tissue, (ii) theinsulative characteristics of the media in the physical gap between theactive electrode(s) and the tissue; (iii) the dimension of the physicalgap between the electrode(s) and the tissue; (iv) the power setting andoptional feedback control of the power level based upon electricalcharacteristics of the targeted tissue; (v) and the translation of theworking end relative to the tissue.

Electrosurgcal Ablation with the Coblator™ System. A recentlycommercialized invention in the field of electrosurgical ablation wasinvented by Eggers et al and is a called Coblator™ system (see. e.g.,disclosures of Eggers et al in U.S. Pat. Nos. 5,873,855; 5,888,198;5,891,095; 6,024,733; 6,032,674; 6,066,134 and the companion patentscited therein). The Coblator™ system relies on the creation of a voltagedifference between a plurality of closely spaced rod-like electrodeelements 2 a and a return electrode 2 b (see FIG. 1B) wherein theworking end carries both the active and return electrodes. The Coblator™system differs from conventional electrosurgical devices in that thesystem introduces an electrically conductive fluid such as isotonicsaline 5 into the physical gaps 6 between the closely spaced activeelectrodes, and between the electrode group and the targeted tissue. Thesystem applies electrical energy with a frequency of about 100 kHz and avoltage of about 100 to 300 V.

The Coblator™ company promotional materials explain that at high voltagelevels, the electrically conductive fluid 5 in the gaps 6 that intervenebetween the closely spaced active electrodes 2 a is converted into anionized vapor or plasma. As evidence of the character of such a plasma,studies have shown that a typical plasma has an orange glow.Spectroscopic analysis of Coblator emissions show an emission peak ofaround 590 nm which is characteristic of the sodium ionization peak(NaCl normal solution used as conductive fluid), with negligibleemissions above 600 nm. The company promotional material claims thatconventional electrosurgical ablation yields a continuous spectrum from490 nm to 900 nm, peaking at around 700 nm.

The supposition underlying the Coblator™ is that the actualenergy-tissue interaction produced by the system relates to chargedparticles in the plasma having sufficient energy to cause dissociationof molecular bonds within tissue structures that come into contact withthe plasma. Based on this hypothesis, the accelerated charged particleshave a very short range of travel, and the energy-tissue interaction isconfined largely to thin surface layers. Further, the supposition isthat the energy-tissue interaction is a “cold” process that does notrely on the thermal vaporization of intra- and extracellular fluids toablate tissue. In this respect, the Coblator™ system has been describedas producing an ablation that compares to that of an excimer laser, bothof which produce similar ablation by-products—if relying on comparisonof spectrographic emission peaks. The energy required to cause molecularbreak-down of common molecular bonds in tissue is believed to be in therange of 3.0 eV to 5.0 eV or more. Considering the amount of energyutilized by the Coblator™ system to initially and thereafter continuallyvaporize NaCl from within a saline solution, it raises the questionwhether the plasma volumes can sustainably provide the energy levelsrequired for true molecular dissociation of compositions in tissuesurfaces, as with an excimer laser.

Another hypothesis that explains the Coblator™ ablation process in moremundane. Referring to FIG. 1B, it can be seen that the Coblator™ workingend traps conductive fluid 5 within the many gaps 6 between the closelyspaces electrode elements. As electrical potential is increased at theelectrodes 2 a, random and dynamic conductive paths are created to thereturn electrode 2 b from random discharge points on the activeelectrodes 2 a. Such conductive paths essentially comprise a dynamicuncontrolled distribution of NaCl molecules in the fluid, that can bemomentarily linked by high energy densities along the conductive paththat will, in turn, vaporize such compositions. The result is a frothyenvironment of random expanding and collapsing bubbles 3 as shown inFIG. 1B. Since the random transient bubbles 5 may comprise aquasi-neutral gas or a substantially insulative gas—thereafter a sparkor discharge path 4 can occur along some random routes between theactive electrode 2 a and the return electrode 2 b and within the bubbles3. As shown in FIG. 1B, when such random insulative bubbles and anelectrical spark path 4 occurs with the tissue surface beingintermediate to the active and return electrodes, a spark-typeenergy-tissue interaction will occur that delivers ablative energy tothe tissue at any random location that a bubble 3 in the path 4interfaces the tissue. While FIG. 1B shows two random spark-type eventsthrough a frothy gas bubble environment, if this hypothesis wereaccepted, an actual Coblator™ ablation comprises 1000's of such randomand discrete spark-type events per second to cause tissue ablation.According to this hypothesis, the Coblator™ system would produce anenergy-tissue interaction much like that of conventional electrosurgicalablation as depicted in FIG. 1A.

This hypothesis easily explains the two observations made by proponentsof the Coblator™ that state (i) that spectroscopic analysis of energydelivery within a conductive fluid supports the theory of moleculardissociation, and (ii) that evidence of limited collateral thermaldamage (so-called “cold” ablation) must be the result of a moleculardissociation process. First, the spectroscopic analysis of the Coblator™ablation certainly would show emission peaks for vaporization of thesodium analytes in the fluid, which is a primary sink of the energyapplied from the device—which is different from and predominates overany emission peaks from the tissue ablation. The tissue ablation, if thecompeting hypothesis of a spark-type interaction of FIG. 1B is accurate,would be characterized by energy-to-tissue events that produce mostlywater vapor from the vaporization of intra- and extracellular fluids.Such vapor would be rapidly absorbed by the surrounding fluidenvironment and might not contribute to any emissions that could beobserved by spectrographic analysis of the bubbles of vaporized NaCl.Second, FIG. 1B depicts that the random discrete spark-type events thatvaporize tissue are brief—occurring in a the very short, random timeintervals in which the insulative bubbles are intact. The lifespan of abubble is likely to have a duration ranging between 100's of ns to 10'sof ms. As is well known, for a tissue ablation to be a substantiallycold process, the intervals between successive thermal energy deliveryevents simply must be longer than the thermal relaxation time of thetissue which is dependent of several tissue characteristics. The thermalrelaxation time also must take into consideration the boundaryconditions. In the Coblator™ process as depicted in FIG. 1B, the thermalrelaxation time of any typical tissue is probably in the range of 100'sof ns. In addition, the fluid comprises a boundary condition that actsas a tremendous heat sink. Since the location of spark-type energyapplications to tissue is random in location and brief in duration, thecombination of (i) the thermal relaxation of the tissue, and (ii) thefluid heat sink removing heat from the tissue can easily return theablated tissue location to a normal temperature before another randomspark-type event occurs in a similar location. Thus, the hypothesis ofmolecular dissociation is not necessary to explain the “coolness” of theablation depicted in FIG. 1B.

The types of ablation caused by conventional electrosurgical ablation(see FIG. 1A) and the type of ablation caused by the Coblator™ system(see FIG. 1B—no matter the hypothesis selected to explain the Coblator™energy-tissue-interaction—share several common characteristics. Whileconventional and the Coblator™ ablations are suitable for manyprocedures, both types of ablation are caused by totally random eventswherein high electrical energy densities vaporize a fluid or elementstherein to create an insulative gas or plasma volume that thereaftercauses random localization of an energy-tissue interaction that ablatestissue. By the term random localization, it is meant that while thegeneral location of tissue ablation is known for any time interval, theexact location of an ablation event, for example for any interval in thens range, is unpredictable. As a further explanation, FIG. 2 representsan enlarged view of a portion of the Coblator™ working end of FIG. 1Bwith a grid in perspective view as the tissue surface. The location atwhich the gas volume, or plasma, interfaces the tissue surface is randomand the application of energy to the surface will be of very lowresolution. If each grid of FIG. 2 is between 10 to 20 μm, the lateraldistance d between the point of energy emission and the point of highestenergy density (herein called the energy deposition or application site)wherein the energy-tissue interaction is localized may as much as 100 to500 μm from a reference axis x of the working end, or the lateraldistance d could be zero. A further graphically depiction of what ismeant by the concept of random localization of energy-tissueinteractions is shown in FIG. 2. In that Figure, the energy deliveryhorizon (or perimeter) is indicated at h, by which is meant that, at ans or ms time-scale, the actual application of energy to the tissue maybe localized anywhere in the delivery horizon h, and the location of anysuch application will be entirely random within this horizon.

Another characteristic common to both conventional electrosurgicalablation (FIG. 1A) and the Coblator™ ablation (FIG. 1B) relates to (i)the random size of and energy contact site and (ii) the randomdistribution of energy across the localized site of energy contact. FIG.2 graphically depicts a random energy contact and ejecta e from suchenergy application being irregularly distributed across the energydeposition site. Since the actual energy application occurs only in adynamic, frothy, expanding and collapsing vapor bubble environment, itis believed that FIG. 2 somewhat accurately depicts the typical energydistribution. In any event, on a ns or ms time-scale, it is clear thatthe dimensions and energy distribution characteristics of energydelivery are uncontrolled and random. This is to be contrasted withlasers energy delivery systems in which localization can be precise witha few μm's and energy distribution across the site can be designed asGaussian (higher energy in center of site) or “top-hat” (even energydistribution across the energy deposition site).

While conventional electrosurgical ablation and Coblator™ type ablationsare suitable for various procedures, the following characteristicscommon to both types of ablation prevent the possibility of more preciseablations with such prior art systems:

(i) the actual energy deposition site is randomly localized instead ofprecisely localized;

(ii) the energy density across the energy deposition site is random anduncontrolled;

(iii) the conductive path between and energy deposition site and theemission point on an electrode is random;

(iv) the dimensions of the energy deposition site are random anduncontrolled;

(v) the amount of energy applied per unit of surface at an energydeposition site is random;

(vi) the amount of energy applied per time interval at an energydeposition site is uncontrolled;

(vii) the duration of intervals between successive energy applicationsto a site are random;

(viii) the actual duration of an interval of energy application israndom and uncontrolled;

(ix) the conductive or insulative characteristics of media between theactive electrode and the targeted site, at a micro-scale, areuncontrolled,

(xi) the dimensions, localization, distribution and duration ofinsulative gas volumes or plasma volumes that facilitate energy deliveryare random and uncontrolled; and

(xii) the prior art instrument working ends function dramaticallydifferently depending on the axial distance between an electrode surfaceand the targeted tissue surface,

It would be highly desirable to have greater precision in thin layerablations for microsurgeries, neurology, and precision skin resurfacingfor burn debridement or cosmetic purposes. What is needed are systemsand methods for selective volumetric removal of body surface layerportions (i) that are precisely controllable; (ii) that do not rely onthermal vaporization effects to ablate tissue; (iii) that can beactivated in a controlled mode that ratably removes depths or volume oftissue in a given time interval to provide selective tissuedecomposition; (iv) that allow for well-defined post treatmentboundaries between layers of tissue decomposition and undamaged layers;(v) that removes surface structure that is exposed to a gas environmentor immersed in a fluid environment; (vi) that provide for energydelivery to a patient's body structure via a working end that can bereduced in scale to less than 1 mm. to 3 mm. in diameter formicro-interventional use; and (vii) that utilize a working end that issimple to manufacture and therefore inexpensive and disposable.

BRIEF SUMMARY OF THE INVENTION

The principal objective of the present invention is to providecontrolled and precise applications of energy to a thin surface layer ofstructure in a patient's body to cause volumetric removal of layerportions substantially without collateral thermal damage. More inparticular, an instrument working end is adapted (i) to deliver highintensity electrical energy in a preferred modality to create a highlyenergetic and dynamic microplasmas for causing molecular volatilizationof surface macromolecules to remove tissue with microscale precision, or(ii) to optionally deliver a spark-type energytissue interaction (hereintermed a conventional electrosurgical ablation modality) but in a novelmicro-scale modality to controllably ablate discrete tissue portions.

The novel energy delivery modalities and energy-tissue interactions arebased on utilizing either of two novel principles (hereafter defined attimes as control principles) in the application of electrical energy tobody structures for ablation purposes. The principles may be applied toa system and instrument working surface independently, or preferably intandem, and are designed to control the numerous factors that to datehave been uncontrolled and random in tissue ablations (i.e., the 12factors listed above at the end of the Section titled Description of theRelated Art.

The first control principle relates to bifurcation of a discreteelectrical energy delivery event into two components. (i) the provisionof electrical potential at an electrode at an intensity level that canablate tissue with the electrode spaced apart from the targeted site;and (ii) the ms or ns (microsecond or nanosecond) control of conductivethe characteristics, or ionization, of selected media in the interfacebetween the electrode and the targeted site. In other words, it ispostulated that the selected media can be switched betweennon-conductive (or insulative) and conductive (or ionized) stated in acontrolled and ultrafast manner to advantageously deliver energy tocause a novel energy-tissue interaction. In a subset of this principle,several ionization methods, as well as energy-enhancing means forenergizing a plasma, are disclosed-with photoionization being apreferred means.

The second control principle relates to a tremendous reduction in scale,or micronization, of the features of the working surface for the purposeof controllably localizing a large number of discrete energy-tissueinteractions, as well as controlling the physical dimensions of plasmavolumes. As will be described below, the working surface may befabricated by semiconductor processing techniques to provide features inthe 5 μm to 10 μm range, by which is meant that widely dispersedmicron-scale electrode elements may each apply electrical energy to alocalized site to provide discrete spaced apart ablation events.Referring to FIG. 4, it is believed that the system and method of theinvention can provide the type of resolution of energy applicationrepresented in FIG. 4, which depicts a controlled, discrete, localizedenergy-tissue interaction eti having a micro-scale dimension (FIG. 4representing a perspective view of a 5 μm to 10 μm grid).

The system is coupled to a computer controller for controlling intervalsof energy delivery-both the ionization means and the electrical energymeans for the ablation-as well as for optional flows of the selectedmedia. By controlling the duration of intervals of energy applicationsand the repetition rate in relation to the thermal relaxation time ofthe targeted surface, it is postulated that the disclosedplasma-assisted tissue removal method will be a substantially coldprocess, ie., there will be substantially no collateral thermal damageto tissue.

Each pulse, or burst, of energy application in the disclosed ablationprocess is assisted or enabled by a sequence of distinct plasmaformation processes to achieve the operational objectives of theinvention, followed by plasma decay intervals. In an initial portion ofthe process, an ionized gas (plasma) is formed to allow subsequentelectrical potential in a spatially-controlled region at the surfacelayer. In a second portion of the process, an electrical discharge iscreated in the ionized gas and surface layer thus causing volatilizationof macromolecules of the targeted surface layers to remove layerportions. To define the uses of plasmas herein, it is useful to providethe following background. A plasma is a quasineutral (partly ionized)gas having a significant proportion of charged particles relative toneutral particles which may, in an equilibrium state, exhibit collectivebehavior. Of interest to this invention are non-equilibrium or highlydynamic microplasmas formed proximate to structure in a patient's bodyto allow for energy transfer to, or deposition of energy within, thinsurface layers of structure in a patient's body to remove (ablate)material without transfer of thermal energy. In the lexicon ofphysicists, a plasma may be defined simply as an ionized gas, todistinguish it from ordinary or neutral gases. In a neutral gas, eachgas atom carries the same number of negatively charged electronsorbiting its nucleus as there are positively charged protons in thatnucleus. While a neutral gas may carry the potential of substantialchemical activity together with dynamic effects (e.g., fluidturbulence), such a neutral gas exhibits little or no response toelectric and magnetic fields—and such neutral gases are substantiallyunable to conduct electrical potential therethrough. A neutral gas,however, can be excited or energized to the plasma state when asufficient proportion of its atoms become ionized by losing one or moreelectrons. Ionization can occur as a result of a number of processes,such as (i) a neutral gas becoming so hot as to cause the atoms tocollide and jar loose electrons (thermal ionization or TI), (ii) aneutral gas being subjected to a high intensity light source thatstrikes the atoms with energetic photons that displace electrons fromtheir orbits (photoionization or PI), (iii) a neutral gas beingsubjected to electric fields that are strong enough to strip awayelectrons from the atoms (field ionization of FI), and (iv) in the caseof non-gaseous materials, a spark or electrical discharge pulse canionize analytes in the surface of a solid.

A resulting plasma (ionized gas) consists of interpenetrating andinteracting accumulations of freely roaming charges (both negative andpositive). This gas state can shift from neutral to ionized byphotoionization or field ionization by the means disclosed herein, it isbelieved, within the range of tens of femtoseconds to hundreds ofpicoseconds. For purposes of this disclosure, the method of forming theinitial plasma (ionized gas) volume involves irradiating a capturedneutral gas volume with a high intensity wavelength (λ) ranging betweenabout 190 nm to 263 nm (or more broadly, within the UV spectrum definedas λ from 10 nm to 400 nm; or, frequency range of 1.0×10¹⁵ Hz to6.0×10¹⁶ Hz). Thereafter, an intense application of energy is applied byto targeted surface layer by creating an ultrafast high-intensityelectrical discharge within the ionized gas volume and the surface layerto cause an electrochemical volatilization of molecules of the surfacelayer, i.e., a plasma-mediated ablation. Each high intensity burst ofelectrical energy forms a critical density plasma at the surface layerthus removing surface material that is ionized. According to thisplasma-mediated form of electrochemical material removal, each energypulse applied to the surface layer when above a certain threshold levelis channeled into to the formation of ejecta (gas plume and fragments)by the volatilization or decomposition of macromolecules of the surfacelayer. The plasma, or microplasma, decays rapidly as ejecta and theplasma transfers heat and energy away from the surface layer and alsoreleases energy in the form of radiative emissions. It is postulatedthat such energy applications to the surface layer (dependent onionization proportion of neutral gas and intensity of the electricaldischarge), can be modeled to provide selective volumetric removal ofmaterial per pulse of energy. In sum, a controllable process forselective volumetric tissue removal is provided by a system including acomputer controller for successively rapid sequencing of (ii)photoionization of a partially-captured neutral gas volume, and (ii)creation of a high-intensity electrical field for volatilization of atargeted thin surface layer.

In the present invention, at sufficiently high energy levels (or voltageV), charged particles in a plasma can possess sufficient energy to breakdown common molecular bonds in macromolecules of a tissue surface. Forexample, such bonds may be carbon-carbon bonds, carbon-nitrogen bonds,etc. It is believed that the energy required to disrupt such bonds iswithin the range of 3.0 eV to 4.0 eV. Preliminary calculations (to berefined for publication in a future disclosure) suggest that theestimated electron energy applied by the inventive system can far exceed4.0 eV when operating at 300 to 1000 volts, making various assumptionsconcerning distances between the active electrode(s) and the targetedsite; and the electron population of the media (gas or liquid) interfacebetween the electrode(s) and the targeted site.

The invention provides a technique for biological material removal thatallows precision of ablation depth by removing a discrete thin layer ofmaterial with optional modes of (i) pulsed applications of intenseenergy to a targeted site, or (ii) the creation of a sustainable highenergy plasma at the interface between a working surface and thetargeted site to cause molecular volatilization.

The invention advantageously provides a control technique forcontrolling material removal by causing a plurality ofmicron-dimensioned energy-tissue interactions over a grid of aninstrument working surface.

The invention advantageously provides a control technique forcontrolling material removal by creating a plurality ofmicron-dimensioned gas volumes that can be switched betweennon-conductive and conductive states for controlling energy applicationsto the targeted tissue surface.

The invention provides a control technique for controlling thedistribution of energy across a targeted site by creating a plurality ofmicron-dimensioned plasma volumes that evenly apply energy acrosstissue.

The invention provides a control technique for enhancing the energy of aplasma to facilitate a plasma-mediated ablation by utilizingelectron-emissive coatings and UV irradiation of a microchannel plate.

The invention advantageously provides a technique for removal of surfacelayers of body structure substantially without collateral thermaldamage.

The invention advantageously provides a technique for ablation (materialremoval) that is generally insensitive to tissue's linear absorptioncharacteristics.

The invention advantageously provides a technique for ablation (materialremoval) that is generally insensitive to tissue hydration.

The invention advantageously provides a technique for ablation ofsurface layers of body structure that is exposed to a gas environment orimmersed in a fluid environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view of a prior art working end of a monopolar probe inrelation to a tissue surface illustrating the method of creatinginsulative gas bubble to cause spark-type discharges to ablate tissue.

FIG. 1B is a view of a prior art working end of a bi-polar probe inrelation to a tissue surface illustrating its the method of ablatingtissue.

FIG. 2 is a sectional view of a portion of the prior art working end ofFIG. 1B depicting the lack of localization of an energy applicationevent.

FIG. 3 is a micron-scaled grid representing a tissue surface thatprovides another view depicting the prior art lack of localization of anenergy application event utilizing the prior art instruments of eitherFIG. 1A or FIG. 1B.

FIG. 4 is a micron-scaled grid representing a tissue surface similar tothat of FIG. 3 that indicates the resolution of energy-tissueinteractions that are possible with the present invention.

FIG. 5 is a plan view of an exemplary probe of the invention in relationto a human hand and a simplified block schematic diagram of the energysources of the system suitable for practice of the principles of theinvention.

FIG. 6 is an enlarged sectional view of the working end of the probe ofFIG. 5 taken along line 6-6 of FIG. 5.

FIGS. 7A-7B are sectional schematic views of alternative shapestructures at a working face of a probe similar to that shown in FIG. 6.

FIGS. 8A-8B are views of a method of practicing the principles of theinvention in a laminectomy/disketomy procedure for treating a herniateddisc; FIG. 8A being a view of introducing the working end of the probeof FIG. 5 into a workspace proximate to the patient's spine; FIG. 8Bbeing an enlarged view of the working end in a portion of a fluid-filledworkspace proximate to surface layers of a targeted structure.

FIGS. 9A-9E are greatly enlarged views of the sequence of steps thatcomprise the method of practicing the principles of the invention forremoving layers of any surface of a body structure immersed in a fluid;FIG. 9A being an illustration of the distal working face in the fluidenvironment; FIG. 9B depicting a neutral gas being introduced into shapestructure of the working face displacing the immersion fluid; FIG. 9Cdepicting irradiation of the neutral gas volume with UV energy therebyphotoionizing the gas in a first (estimated) ps time interval; FIG. 9Ddepicting an initial (estimated) ps time interval in creating ahigh-intensity electrical field in the ionized gas volume to create aplasma and thereby ablating tissue; FIG. 9E depicting a subsequent timeinterval wherein the sequence of events begin to be repeated as theneutral gas is introduced into the working face.

FIG. 10 is a perspective view of the working end of an exemplary Type“C” system of the invention and its use in a skin resurfacing procedure.

FIG. 11 is a sectional view of the working end of FIG. 10 showing themicrochannel structure of the working surface and a block schematicdiagram of the energy sources of the system.

FIG. 12 is a greatly enlarged sectional view of the working end of FIG.11 showing the microchannel structure of the working surface in moredetail.

FIG. 13 is an enlarged sectional view of a single microchannel similarto FIG. 12 showing an optional electronemissive coating added to theproximal region of the microchannel structure.

FIG. 14A is a view of an exemplary micro-scale gas volume without thesurrounding structure of the working surface that illustrates a surfaceengagement plane about the volume and the area that engages anelectrode.

FIG. 14B is another view of the exemplary micro-scale gas volume of FIG.14A shown in a relation to a microchannel with a surrounding gasenvironment also depicted graphically.

FIGS. 15A-15E are views of a first mode of practicing the principles ofthe invention with the Type “C” system of FIGS. 11-12:

FIG. 15A is a view of a plurality of microchannel terminations with thesurrounding structure of the working surface in phantom view in relationto a micron-dimensioned grid representing the targeted site, and furtherdepicting the step of creating electrical potential at the electrodes;

FIG. 15B is a view of the plurality of introduced media volumes similarto FIG. 14A after the step of ionization of the volumes by a UV sourcewith the ionization graphically depicted as shading;

FIG. 15C is a similar to that of FIG. 15B this time depicting thetransient (ionized) conductive path in the surrounding gas media that isextended distally from the working surface.

FIG. 15D is similar to FIG. 15B and occurs substantially contemporaneouswith the ionization of FIG. 15B at which time the electrical potentialat the electrode controllably applies energy across the ionized mediavolume to the targeted site.

FIG. 15E follows FIG. 15D after a brief interval (estimated at 10's ofns) and depicts the material removal process (not-to-scale) wherein theapplication of energy cause volumetric material removal resulting in anejecta plume into the remnants of the ionized gas media.

FIG. 16A is a graphical view of a “top hat” energy distribution across alaser energy-tissue interaction.

FIG. 16B is a graphical view of a Gaussian energy distribution across alaser energy-tissue interaction.

FIG. 17 is a view of a second mode of practicing the principles of theinvention with the Type “C” system by utilizing electron emissions froma microchannel plate (MCP) to energize the gas volumes depicted in FIG.11 to achieve a plasma-mediated ablation.

FIG. 18 is a view of an alternative embodiment of working end forpracticing the method of FIG. 17 in which multiple MCP's are arranged ina chevron pattern to further enhance an electron avalanche in plasmavolumes.

FIG. 19A is a view of the distal end of another probe member thatcarries a microchannel plate structure similar to that of FIG. 11, thistime utilizing field ionization of captured gas volumes, the working endadapted for thin layer ablation of mucosal layers.

FIG. 19B is a sectional view of the distal end of the probe member ofFIG. 19A.

FIG. 19C is a greatly enlarged sectional view of the working end of theprobe member of FIG. 19B showing the microchannel structure.

FIG. 19D is a view of practicing the principles of the invention withthe working end of FIG. 19C using field ionization means to switch thegas volumes flowing through the microchannel structure betweenconductive and nonconductive states.

FIG. 20 is a cut-away view of a working surface of an exemplary Type “D”system which is similar to the Type “C” system except for the use ofmultiple out-of-phase electrodes to insure continuous high voltageenergy delivery to a plasma for plasma mediated ablations.

FIG. 21 is a sectional view of a working surface similar to that of FIG.20 adapted for functioning without the neutral gas inflows throughopen-ended microchannels.

FIG. 22A is a sectional view of a working surface of a Type “E” systemwith the addition of a vibration source coupled to thereto.

FIG. 22B is another sectional view of the working surface of FIG. 22Aillustrating a method use.

FIG. 23 is a sectional view of a working surface of another Type “E”system that uses ultrasonic energy to create cavitation that cooperateswith electrical energy application to the targeted tissue.

DETAILED DESCRIPTION OF THE INVENTION

I. Operational Principles of Plasma-Assisted Cold Ablation of ThinSurface Layers

The several principles of operation of an exemplary plasma-mediatedablation system 5 (see FIG. 5) for the ratable removal of thin surfacelayers will be described in detail in the following sections inconnection with an exemplary procedure: the selective removal oftargeted tissue that is proximate to a delicate structure such as anerve (e.g., material removal in a larninectomy/disketomy procedure fortreating a herniated disc). The following description of the operationthe probe of FIGS. 5-6 and the techniques of FIGS. 9A-9B and 9A-9F arefor exemplary purposes only and are not intended to limit theapplication of the system and methods of the invention. As will bedescribed in further detail herein, the system may have application in awide variety of surface layer ablations and volumetric tissue removalprocedures. The system 5, which may be described herein as a PASCALsystem (plasma-assisted cold ablation layer-by layer), is developed inaccordance with the following operational principles, which will bedescribed seriatim. The PASCAL system provides: (A) ultrafast pulses ofenergy applied to thin surface layers to create critical densitymicroplasma events without transfer of thermal energy, (B) confinementmeans for at least partially confining a nonequilibrium microplasmaformed by photoionization to allow electrical potential therein tothereby allow energy application by an electrical source (as opposed tolaser source), (C) control means for controlling pulse duration and therepetition of energy application events to provide layer-by-layervolumetric material removal; and (D) feedback control systems (optional)based on analysis of plasma luminescence caused by the plasma-mediatedablation process.

A. Operational Principle: Ultrafast Pulsed Energy Application forVolatilization of Surface Layers.

A first objective of the present invention is to provide an ultrafastpulsed application of electrical energy to a targeted site on a surfacelayer of structure in a patient's body. In this invention, each discreteapplication of energy (pulse or burst) can be defined by quantity ofenergy (J) and a duration in which such energy is deposited within thesurface layer. A first operational principal of the invention is that,for a given energy quantity in joules, the duration of energyapplication is less than a threshold electron-to-lattice energy transfertime for the surface layer of the targeted structure. It is postulatedthat for surface layers of structures here in question, thischaracteristic energy transfer time is in the range of about 10 ps to100 ps. Thus, when a high-intensity pulse of energy is applied in asub-threshold duration, the mechanism of layer removal can becharacterized as a chemical alteration of surface molecules, or morespecifically an electrochemical-tissue interaction since the energy isapplied by means of an intense electrical field. In contrast, if thepulse duration of energy application is at an above-threshold level(e.g., in the ms range) with sufficient energy to cause damage, themechanism and characteristics such of ablation would differ. That is,above-threshold energy delivery would cause damage that is largelythermal in nature and characterized by vaporization, melting,denaturation, fracture, etc. (In this above-threshold energy deliverymodality, the electron kinetic energy transfer to the material's latticestructure is dependent on thermal diffusivity, a material property whichexpresses the ability of heat to diffuse and is equal to the square rootof the ratio between heat conductivity and specific heat capacity). Thepresent invention, however, is directed to ultrafast pulses(subthreshold duration) of energy application that create a criticaldensity plasma from a thin surface layer. More specifically, theintensity of the electrical field (or discharge) and its absorption inthe surface layer results in volatilization of macromolecules in thelayer thus causing actual ionization of the thin layer thereby removingbulk. The energy burst is absorbed non-linearly and produces quasi-freeelectrons which, in turn, may act as seed electrons to cause an electronavalanche by various ionization processes. (Various ionization processesfall within the scope of the practice of the method, e.g., collisionalionization, multiphoton ionization, and field ionization). Theseionization processes lead to irreversible alteration in the surface ofthe structure as ejecta (gas and bulk material) is ejected from thelayer. It is believed that a very high fraction of the applied energy isremoved by the high-velocity ejecta. Thus, any instantaneous hightemperatures caused by the energy application are removed from the layerby the plasma formation process. It is further believed that mechanicalshock waves to the bulk material will be insignificant compared toenergy applications at above-threshold levels as defined above. At thesubthreshold energy duration applications proposed herein in accordancewith practice of the method, there will be insufficient time for latticecoupling, thus resulting in insignificant thermal diffusion-inducedcollateral damage to the structure.

A further desirable consequence of using such ultrafast pulse of energyapplication for surface layer removal is that the method is relativelyinsensitive to hydration and density of the targeted surface layer, andis entirely chromophore independent. The drawback to the layer-by-layerplasma-mediated process disclosed herein is that the ablation rate,defined generally as the depth of layer removal per pulse, is small.That is, each pulsed energy application will only remove a layer havinga thickness measured in μm's (microns). It is postulated that layerremoval rate will range from about 1 μm to about 200 μm within theanticipated energy application parameters (from 0.1 J/cm.² to 1000J/cm.²; or 0.1 J to 10 J per pulse). In order to overcome the low ratesof material removal per pulse of energy in the typical case that needssubstantial volumetric removal, the repetition rate of pulsed energyapplication must be high. This operational principle of the inventionwill be described below in Section I(C).

B. Operational Principle: Photoionization of Neutral Gas and Confinementby Shape Structure and/or Fluid.

The previous Section I(A) described a means for plasma-mediated coldelectrochemical ablation of layers of body structure, but to construct asystem feasible for surgical use, it is necessary define operationalprinciples for spatial control of the energy application at the targetedlayer to cause molecular volatilization. The operational principlesaccording to this aspect of the invention relate to (i) providing meansfor creating an electrically conductive (partially ionized) gas volumeproximate to the layer that is targeted, since the plasma-mediatedablation process described in Section I(A) can only occur in such acondition; and (ii) providing means for at least partially confining theionized gas volume in its non-equilibrium state for a sufficient timeinterval to create the intense electrical field therein to causevolumetric removal.

The present invention utilizes a probe with a distal working surfacethat in placed proximate to the targeted site for energy delivery. Thus,it is necessary to create the non-equilibrium ionized gas (an initialplasma) generally about this working surface. The invention utilizes aconcept novel to biomedical applications for photoionizing a neutral gasvolume introduced to the working surface. In such photoionization, ahigh-energy photon (e.g., from a UV source) irradiating the neutral gasmay interact with an ionic electron leading to removal of that electronfrom the ion. To photoionize an ion requires a photon energy greaterthan the binding energy of the electron. As photons increase in energy(wavelength dependent), the cross-section for photoionization of aparticular electronic state is zero until at a certain point thecross-section jumps to a finite value, which is termed a photoelectricedge. The method of the invention thus selects a radiation sourcecharacterized by photon/wavelength energies beyond the photoelectricedge as it relates to the selected neutral gas composition (for purposesof the disclosure, the gas may be any ionizable gas compatible withbiomedical application, e.g., air, nitrogen, oxygen, CO₂, etc.). In thecase of such photoionization, the departing electrons must exchangevirtual photons with the nuclei for the process to occur. Suchphotoionization, therefore, tends to preferentially remove inner-shell(i.e., K-shell) electrons since these can most readily interact with thenucleus. Due to this effect, this process general leaves highly excitedions. After photoionization by photons of energy, the liberatedelectrons possess a kinetic energy and successive electron-electroncollisions distribute this energy throughout the electron populationwith such kinetic energy being thermalised into a surrounding plasma.The non-equilibrium plasma thus created at the working surface of theprobe and at the surface layer is capable of interfacing an intenseelectrical field (electrical discharge) with the targeted layer to causethe electrochemical ablation described in Section I(A). It is postulatedthat the photoionization of the neutral gas volume occurs within fs orps and the duration of UV light pulse for such photoioization isdescribed below in Section I(C) relating to repetition rates

In accordance with practicing this method of creating a photoionized gasvolume (non-equilibrium plasma), another aspect of the invention relatesto confining or containing the ionized gas in its non-equilibrium stateproximate to, or in contact with, the layer targeted for ablation.Essentially, two operational principles are employed to maintain theplasma's condition for sufficient duration to allow the high-intensityelectrical discharge therethrough. First, the targeted surface layer ispreferably immersed in a fluid environment (the fluid being any suitablewater, non-conductive water-based solution or a saline solution, or ahydrogel) to prevent the ionized gas from rapid dispersion into thesurrounding environment. In a surgery in the interior of a patient'sbody, such as an arthroscopic procedure, the standard use of salineimmersion is compatible with the invention. By the term immersion, it ismeant that the surface layer is covered in any suitable fluid to anyparticular depth, and the depth may be very slight and still accomplishthe purpose of preventing dispersion of the ionized gas volume. Forexample, the fluid immersion may comprise a layer as thin as a film ifit provides a seal between a perimeter of the working face and targetedlayer to briefly contain the plasma. Thus, the method of the inventionmay be used on surface layers of body structure exposed to theatmosphere, such as a patient's skin, when covering the structure with athin gel or water.

A second (optional) principle that is utilized to confine the plasma isthe provision of a shape structure at the working surface of the probe,such as a concavity to at least partially confine the photoionized gas.This shape structure also is useful for controlling the volume ofionized gas which will play a role in the plasma-mediated transfer ofenergy to the targeted surface layer. This shape structure, as well asparticular dimensions of an exemplary embodiment, will be described inSection II below.

C. Operational Principle: Controlled High Repetition Rate of PulsedEnergy Applications.

The above Sections described a novel pulsed plasma-mediated ablationprocess that occurs, per pulse, in a time interval that may range frompicoseconds to microseconds. In the sequential energy deliveries andplasma formations, only a thin layer of tissue is removed by theelectrochemical-tissue interaction. In order to provide functionalvolumetric removal, the ultrafast pulsed energy event must be repeatedat a high rate, and this Section describes operational principlesrelating to the selection of such a repetition rate. At a theoreticalhigh repetition rate, there will be a high rate of volumetric removal.However, if the repetition rate is too high there may be collateraldamage from thermal effects conducted to the surface layer by theplasma, which would defeat the objective of the invention in providing asubstantially cold volumetric removal process. While it is postulatedthat the electrochemical-tissue interaction will occur withoutsubstantial thermal effects, a succession of ultrafast plasma creationand decay events may build up thermal effects in the plasma that wouldbe conducted to the surface layer thus being capable of causingcollateral thermal damage.

The operational principle in determining a maximum theoreticalrepetition rate for pulsed energy applications concerns the relationshipbetween duration of energy absorption effects by the surface layer andthe layer's confinement of heat, which thus may result in unwantedcollateral thermal damage. The operative construct is the so-calledthermal relaxation time, and is defined as the time required forsignificant cooling of a defined volume of a body structure that hasbeen elevated in temperature. Thermal relaxation is often defined as thetime required for an elevated tissue temperature to be reduced by 50percent. Many processes are involved in such cooling, such asconduction, convection and radiation. Macroscale conduction cooling inbody structures probably dominates, but microscale radiational coolingat a very small target site proximate to a plasma may be important. Fortargeted sites on structure in a patient's body in laser applications,the rule of thumb is that the thermal relaxation time in secondsapproximately equals the squared dimension of the targeted site in mm.(For example, a 0.5 μm size structure (5×10.⁻⁴ mm.) will substantiallycool in about 250 ns (25×10.⁻⁸ seconds)). In the case of the inventivemethod disclosed herein, the fluid immersion aspect of the method isadvantageous and will help provide rapid thermal relaxation. The fluidfurther may be pre-cooled which is beyond the scope of this disclosure.

In accordance with practicing the principles of the method, it ispostulated that ultrafast pulses of energy will be absorbed in the rangeof 100's of ps to 100's of ns. It is further postulated that repetitionrates in the range of from about 10 Hz to about 500 Hz (or even 1000 Hz)are possible without exceeding the relaxation time of the surface layer.At this time, the repetition rates are theoretical and are to beexplored with bench tests. As a practical matter, the timing ofcontrolled flows of a neutral gas to the working surface and irradiationof the gas volume may prevent extremely high repetition rates. It isbelieved that with repetition rates in range of 2 Hz to 100 Hz, layerremoval rates could be as high a 1 mm./s while maintaining the desiredminimal collateral damage characteristics of the plasma-mediatedablation.

D. Operational Principle: Plasma Luminescence Feedback System for TissueLayer Differentiation.

A final operational principle underlying the practice of plasma-mediatedablation relates to the potential need for diagnostic means in theselective layer removal process to prevent the removal of layers ofstructures that must be protected. In many procedures relating to tissueremoval by a surgeon, the ablation process will be initiated andterminated on the basis of the surgeon's visual observation of thetargeted surface layer and evaluation of the ablation process. However,when ablating surface layers in the interior of a patient's body,particularly in a fluid environment, endoscopic observation of theablation process may be poor. A principal reason for the author'sinvestigation of plasma-mediated ablation in a fluid environment is thatthe inventive method advantageously will allow spectroscopic analysis ofluminescence of the plasma, and control signals may be derived therefromto terminate the ablation process. In other words, as each successiveplasma is formed by the pulsed high-intensity electrical discharge, anopportunity is provided to use tissue layer differentiation diagnosticprocedures based on spectroscopic plasma emission signatures. Such aspectroscopy system would utilize an optic fiber for collecting emittedlight from the plasma generated by the volatilization of the surfacelayer and ejecta in the plasma. The light would be dispersed andanalyzed by an analyzer system, such as an intensified, gated, opticalmulti-channel analyzer/spectrograph. Emission peaks characteristic ofdifferent tissue types would be used as reference data within theanalyzer system. Thus, when the system detected emission characteristicsof material that is not targeted, a signal would be provided to thecontroller to terminate the ablation process. It is believed this typeof feedback system is novel to any electrosurgical ablation modality,and is made possible only because the practice of the method includesthe creation of successive microplasmas at the targeted site. Further,this type feedback signal system is novel in that it can be utilized ina fluid operating environment. (Optical feedback systems based onspectroscopy have been tested with forms of laser energy delivery, butsuch laser systems cannot operate in a fluid environment. See, e.g., B.M. Kim, M. D. Feit, A. M. Rubenchik, B. M. Mammini & L. B. Da Silva,Optical feedback signal for ultra short pulse ablation of tissue, Appl.Surface Sci. 127-129(1998) pp. 857-862.)

II. Construction of Exemplary Type “A” System for Plasma-Assisted ColdAblation

Referring to FIG. 5, an exemplary Type “A” embodiment of PASCAL system 5is shown which includes probe 10 and a remote energy sources in blockdiagrams. In this disclosure, the working surface 15 of probe 10 isadapted for positioning proximate to a targeted site on a surface layerof body structure to accomplish cold plasma-mediated ablation of thelayer. The term ablation is used to characterize the surface layerremoval process, and other descriptive words may be used interchangeablyherein, such as, breakdown, decomposition, disintegration, obliteration,removal and volumetric removal to describe and define theplasma-mediated process that causes layers of a structure in, or on, abody to be altered, broken down, destroyed, damaged, or fragmented andejected from the surface layer. The term structure of a patient's bodyas used herein is intended to be inclusive of any composition in apatient's body, and principally encompasses biological tissues but alsois intended to describe all other body structures (some of which aresometimes not termed tissue) such as calculi, accretions, deposits,occlusions, bones and teeth, and the like.

The exemplary probe 10 of the system comprises an elongate extensionmember 20 having proximal (handle) end 21 and a distal working surfaceend indicated at 15 with a cross-section or diameter of body 22 beingabout from 1.0 mm. to 5.0 mm. (not limiting), the extension memberdefining longitudinal axis 27. The extension member may be fabricated ina variety of configurations to mechanically support at least one activeelectrode about in the working surface 15 and to allow the operator toposition the working surface 15 in relation to a targeted site on asurface layer by manual or robotic manipulation of the proximal end 21of the extension member. Typically, the extension member 20 comprises asmall cross-section member or tube being dimensioned for introductioninto the interior of a patient's body through a trocar (cannula) in aminimally invasive procedure, for example in arthroscopy, laparoscopy,or another thoracoscopic or endoscopic procedure. The elongate membermay have any suitable length. The elongate member also may be rigid orflexible. A flexible probe may be provided with pull wires, shape memoryactuators, and other mechanisms known in the art for articulating adistal end for positioning the working face proximate to the targetedsite.

In FIG. 6, it can be seen that working surface 15 defines a shapestructure 28 comprising a concave or recessed portion 30. The recessedshape structure 28 is adapted to at least partially contain a neutralgas and its photoionized counterpart and the concavity may be of anysuitable dimension or extend inwardly (proximally) to an interiorchamber portion 32 and fall within the scope of the invention. FIGS.7A-7B show sectional silhouettes of alternative shape structures 28 withFIG. 7A depicting a more concave shape structure suitable for use in animmersion fluid F in a workspace WS over tissue layer L and FIG. 7Bshowing a slight concavity (a lack of concavity altogether may fallwithin the scope of the invention) for use with a more viscous fluid VFor gel layer over tissue layer L.

Returning to FIG. 6, probe 10 carries a optical delivery orlight-channeling means such as an optical fiber 35 (or fiber opticbundle, wave guide or other light-channeling means) in central portion37 of extension member 10 which is adapted to direct light energy from ahigh-intensity source or UV source 40 as described above in SectionI(B). The optical delivery subsystem depends on the design parameters ofthe tissue removal system and may alternatively comprise a fiber opticcable, an articulated arm with mirrors, or an open beam delivery systemincluding coated reflectors and lenses to focus the radiative beam. Inthis embodiment, the optic fiber with cladding 42 is carried in centrallumen 44 of the extension member 20. In any event, the working surface15 is carried at a distal end of probe 10 to allow the operator tomaneuver the working surface into proximity to a targeted surface layer.It should be appreciated that the distal termination of the fiber 35 mayhave its cladding 42 partly removed (not shown) to cause photoionizationalong a distal portion of passageway or lumen 44.

A computer controller 45 is operatively connected to the high-intensitylight source 40, and controls the activation of the source, as well asits pulse repetition rate, in response to control signals that areprovided by the system operator. Any sort of on-off switch (foot pedalor hand switch not shown) is connected to controller 45 and providesactivation signals in response to the actuation of the switch. The pulserepetition rate may be set by the operator by a form of rheostat controlconnected to controller 45 which increases or decreases the repetitionrate in response to the operator selection. It should be appreciatedthat any suitable high-intensity UV source 40 may be suitable fordelivering energy along the light-channeling means 35, and aconventional discharge lamp known in the art is preferred together withoptional filters, combiners, and associated optics may be suitable toperform the method of photoionization aspect of the method describedabove (i.e, a discharge lamp passes an electric current through a raregas or metal vapor, wherein electrons collide with gas atoms excitingthem to higher energy levels which then decay to lower levels byemitting light; mercury, hydrogen, deuterium, Ne, Ar, Kr, and Xedischarge lamps all may useful for the photoionization aspect of themethod). The light source is preferably remote and carried to probe 10by a flexible fiber (not shown) but the light source also could becarried in a handle portion of the probe. The light source 40 also maybe an excimer laser, such as an OPTex system by Lambda Physik, Inc.,3201 West Commercial Blvd., Ft. Lauderdale, Fla.

The UV energy radiated from source 40 is pulsed as is known in the artby a computer controller 45 capable of controlling the delivery of lightpulses having a pulse duration ranging from about 100 ps to tens of mswith a repetition rate ranging from about 1 Hz to 1000 Hz. In theexemplary embodiment of FIG. 6, extension member 20 may carry a singleoptical fiber or a fiber bundle having any suitable diameter, forexample ranging from about 100 μm to 500 μm.

FIG. 6 further shows a neutral gas delivery source 50 that communicateswith the interior lumen 44 or passageway in member 20 that is configuredconcentrically around fiber 35. The lumen 44 extends to its distalterminus 52 at the interface with the concavity or shape structure 28with web portions 54 a and opening portions 54 b maintaining the fiberin a central portion of lumen 44. It should be appreciated that anyfluid-tight passageway may be provided and it need not be a concentricrelative to the light channeling means 35. The system further provides apositive (+) pressurization system indicated at 55 for moving theneutral gas to the working surface 25 and may include any pump means orgas metering means known in the art, such as a peristaltic pump. Asillustrated in FIG. 5, the neutral gas pressurization system 55 isoperatively connected to the controller 45 for timing gas inflows, orpulsed inflows, relative to the irradiation of the gas volume withphotonic energy from the photoionizing source 40.

Referring to FIGS. 5-6, an electrical source 60 is provided as theenergy delivery means to perform the electrochemical ablation, and theintense electrical field in the photoionized gas volume is created viaan electrode arrangement indicated at 65. The exemplary activeconductive electrode 65 of FIG. 6 is carried in the concave shapestructure 28 of the working face 15. In accordance with the practice ofthe invention, the electrode arrangement 65 will have one active surfaceportion 66 with a particular surface geometry shape that is adapted toenhance the intensity of the electric field and the current density atthe time of each pulsed energy delivery. For this reason, such surfacegeometry preferably includes at least one projecting portion or sharpedge portion at the active surface. In the exemplary embodiment of FIG.6, the surface geometry is characterized by a plurality of twoprojecting sharp edges 66A-66B that extend into the concave shapestructure 28 of working face 15. It should be appreciated such preferredsurface geometry may include only one conductive electrode portion, or aplurality of micro-scale sharp edges that may be characterized simply assurface roughness on the active surface of the electrode, and as suchmay be provided by any suitable chemical, electrochemical or abrasivemethod to create micro-edges on the active surface portion to thusenhance the high electric field intensities between the active electrodesurface 66 and the targeted surface layer. In any type of electrodearrangement, the electrodes edges or projecting portion may be isolatedbut are the same source polarity as they will be electrically coupled towith a common electrical lead 67 either in the proximal end 21 of theextension member or at the electrical source 60. The exemplary activeelectrode 65 is shown as extending around axis 27 of the concave portion28 but it should be appreciated that the electrode could be located atany other suitable location about the working surface. Referring stillto FIG. 6, the electrode 65 is coupled to a conductive lead or wireelement 67 that extends through body portion 22 of elongate member 20.The body portion 22 of extension member 10 may be any suitable insulatedmaterial such as a ceramic, plastic, glass or a combination of separateelements as are known in the art.

In the block diagram portion of FIG. 5, it can be seen that the system 5has an electrical source 60 that is connected to electrode arrangement65. The electrical source 60 may be any suitable electrical energysource as is known in the art than is capable of delivering highintensity electrical current, for example in the range of 10 to 2000volts. The electrical source 60 of the present invention preferablydelivers a high frequency voltage that may be selected from a range togenerate average power levels ranging from a few milliwatts to hundredsof watts depending on the targeted surface layer and the desired therate of removal. The controller 45 associated with the electrical source60 would allow the operator to select the voltage level according to thespecific requirements of surface layer removal procedure. It ispostulated that the voltage applied between the active electrode and thesurface layer and return electrode will be in the range from about 50volts to 2000 volts. The electrical source 60 is coupled to computercontroller 45 to control the timing of energy delivery in relation tothe timing of the photoionization step, and also may be programmed withsuitable software 72 to allow independent modulation of parameters ofelectrical energy delivery, including: (i) voltage, current and peakelectrical power per time interval; (ii) the length of a time intervalof current delivery; and (iii) the profile of energy delivery withineach time interval, to allow 1 to 1000 Hz repetition rates.

The computer controller 45 of the invention depicted in FIG. 5 mayfurther be provided with feed-back circuitry known in the art formeasuring the impedance between the active electrode surface 66 and thetargeted surface layer. The impedance level will change, as will bedescribed in the steps of the method shown below in Section III, as theneutral gas volume is photoionized, and thus feedback of the change inimpedance can be used as a control signal for initiating the step ofhigh-energy electrical energy delivery.

III. Method of Use of Type “A” System for Plasma-Assisted Cold Ablationof Surface Layers.

In practicing the method of the invention in a laminectomy/disketomyprocedure to treat a herniated disc by removing surface layers oftissue, the patient is be prepared in any conventional manner withanesthetics and FIG. 8A depicts the elongate extension member 20 and itsworking face 15 being advanced into a working space WS to the targetedlayer L. The surgeon may advance the working face 15 under endoscopicvision or by other manners known in the art (not shown), such as beingassisted by real-time imaging. FIG. 8B represents an enlarged view ofthe working face 15 in a workspace that is filled with a fluid 80. FIGS.8B & 9A-9E show that the patient's body is coupled to a ground pad orreturn (−) electrode 85 as is known in the art.

Now referring to FIG. 9A, a sectional view of the distal end ofextension member 20 is shown positioned proximate (within about 1 mm. orless), or pressed gently against the targeted layer L (it should beappreciated that layer L may be the surface layer of any bodystructure). FIG. 9B then shows actuation of the system by controller 45wherein a neutral gas NG is introduced through lumen 44 into the workingface 15 with the volume being captured by the concave shape structure 28and the surrounding fluid 80 which prevents the gas from rapidlydispersing.

Now turning to FIG. 9C, the controller 45 after a pre-selected timeinterval irradiates the neutral gas volume with UV energy via beam 82that is carried through optic fiber 35 from source 40. FIG. 9C thusdepicts the step of photoionizing the neutral gas volume to create aconductive plasma indicated at P₁ that will remain in suchnon-equilibrium state for a first brief time interval. In FIG. 9D, thecontroller 45, after a pre-selected very brief time interval, triggersthe power source 60 to deliver an intense electrical energy pulse fromthe active electrode surface 66 across the plasma to layer L (that iscoupled to return electrode). FIG. 9D thus depicts the volatilization orcommencement of ionization of layer L which, in effect, begins to alterthe condition with other species to form an altered plasma indicated atP₂. In FIG. 9D, the volatilization of the surface layer L removesmaterial from the layer by application of an energy quantity to thelayer with ejecta E depicted in the plasma P₂, wherein the ejecta isessentially gases and possibly material fragments (depth of materialremoval exaggerated in FIG. 9D for a single plasma creation event). In avery brief time interval subsequent to the ultrafast fast event depictedin FIG. 9D, the plasma P₂ will decay. Thereafter a repetition of theplasma-mediated material removal process occurs as the controller 45repeats the plasma-mediated ablative pulses in accordance with theevents depicted in FIGS. 9A-9D. FIG. 9E shows the next step in thissequence with the neutral gas NG being introduced into the working face15. It should be appreciated that the probe may be translated acrosslayer L to remove material in a path or maintained in a stationary todrill a hole in the layer, either of which may be an element of theprocedure. The distalmost surface of the probe preferably is to be heldgently against the tissue layer, of slightly above the tissue layer In adiskectomy procedure as indicated in FIG. 9A, material is removed asrequired under endoscopic visualization, without thermal collateraldamage to surrounding tissue.

The method of the invention may further include the step of analyzingthe emission spectra by means of the fiber optic 35 which is coupled toa remote plasma luminescence spectroscopy system and controller 45. Forexample, the plume following a ultrafast plasma creation event inremoving disc material in the exemplary procedure will provide emissionsthat can be compared with reference data for a known material in a disc,such as calcium If the emissions from the plasma exhibit characteristicsthat compare with non-targeted disc material, such as a nerve, thespectroscopy system can signal the controller 45 to terminate energydelivery.

IV. Construction of Type “B” System for Plasma-Assisted Cold Ablation.

A Type “B” embodiment (not shown) is very similar to the Type “A”embodiment except that the central core of the probe carries an opticfiber that is utilized to collect emitted light emissions from theplasma P₂ indicated in FIGS. 9D-9E. The emission peaks of the plasma P₂are fed to a spectroscopic analyzer system 90 (see FIG. 5) and comparedto the peaks in reference data to determine whether non-targeted tissuetypes have been affected by the ablation. The system is connected tocontroller 45 and may be programmed to terminate the ablation processwithin ns or ms.

The Type “B” system also includes impedance-measuring circuitry fortriggering the delivery of electrical energy to the (photoionized gas)plasma P₁ as indicated in FIG. 9C. In other words, instead of providingprogramming in controller 45 that triggers energy delivery in apre-selected time sequence, the impedance-measuring circuitry cancontinuously measure impedance within the region between the activeelectrode surface 66 and layer L which is altered by (i) thephotoionization of the neutral gas volume as shown in FIG. 9C as well asits confinement, and (ii) the distance between the working face 15 andlayer L.

Another aspect of the Type “B” embodiment of the invention (not shown)is the provision for aspiration of ejecta and fluid from the workspace.For example, if the targeted layer is a portion of malignant tissue, itmay be useful to sequence aspiration of the ablated tissue fragments(along with gas and fluid) from the workspace. The controller would beadapted to provide such pulsed aspiration between pulsed applications ofenergy. The passageway for receiving such removed material particleswould preferably be a concentric lumen around the extension member 20 ofFIG. 6, but it could also be any type of interior passageway and fallwithin the scope of the invention.

V. Construction and Method of Use of Exemplary Type “C” System forPlasma-Assisted Material Removal.

In a previous part of this disclosure (see “Summary and Objects of theInvention”), a number of processes were described to cause, induce ordevelop ionization of a captured neutral gas volume (or bubble), andthereafter terminate ionization of the gas, in an interface between aprobe working end and a targeted site ts. Such an instantaneously andindependently ionized gas volume can then cause an intense applicationor arc of electrical energy from an electrode to the targeted site tsacross the gas volume to volumetrically remove surface layers of ananatomic structure. Several ionization processes were described above,viz., photoionization (PI), field ionization (FI), thermal ionization(TI) and the ionization of surface analytes from a solid material. Inthis Type “C” embodiment 205, the use of independent field ionization(FI) means is described as an option in Section V(C) below and at timesreferred to as the first energy source. In addition, a working endcarrying a microchannel plate (MCP) is disclosed in Section V(B) belowwhich comprises an electron-emissive coating on a microchannel structurethat, it is postulated, can enhance the energy of a plasma for causingvolumetric material removal. Both the Type “A” and “C” systems utilizethe same gas source 50 for introducing the neutral gas volume to workingsurface. The Type “C” system also is coupled to controller 45 andelectrical source 60 (second energy source) as described above thatallows for the time-controlled and volume-metered introduction of theneutral gas volume (media m₂) to the working end. All parameters ofelectrical energy delivery may be programmed to generate trains ofenergy applications to the targeted site ts at selected repetitionrates, or in a continuous mode, as described in the Type “A” systemabove.

A. Intense Pulsed Electric Discharge Mode of Operation of Type “C”Working End

More in particular, the Type “C” system of FIGS. 10 and 11 depicts anexemplary working end 210 of a probe member 212 that is adapted for usein a skin resurfacing procedure. For example, FIG. 10 shows the workingend being translated over a skin surface very close to a patient's eye,which may be problematic for laser resurfacing. As will be describedbelow, energy applied by the working surface to the skin can bemodulated easily to cause very thin layer ablations for sensitive areas,such as periocular regions, in manners not possible with a laser. Also,the same instrument may deliver a first selected intensity of energy tothe main portions of the patient's face, and a second selected energyintensity to periocular regions. FIGS. 10-11 show the exemplary workingend with a narrow width-of-face dimension indicated at wf in comparisonto a length-of-face dimension If across the working surface 215. In aninstrument adapted for unidirectional translation or painting acrosstissue, such as in skin resurfacing, it is preferable to have such anarrow width with substantially parallel sides (transverse to thedirection of translation) to control the number of successiveenergy-tissue interactions that occur as the working face 215 passesover any location. As will be described below, any width dimensionacross a working face may be defined by the number of features (ormicrochannels) at which a discrete energy-tissue interactions arelocalized.

In this Type “C” system 205, an exemplary working end 210 of a probemember 212 (see FIGS. 11 & 12) has a working surface 215 that carries amicrochannel structure comprising of a plurality of channels (e.g., 220a-220 d in FIG. 12) having open distal terminations 222 a-222 d in theworking surface. The microchannel structure can be fabricated by thesame processes as a micro-channel plate (MCP) or may be fabricated by aplasma-processing means known in the MEMS field (microelectricalmachining). The insulator material 224 of the working surface may beglass, plastic, ceramic, a form of silicon or any other suitablematerial. As an example of fabricating the microchannels, a microchannelplate (NCP) is a device that is commercially available forphoto-detection purposes and may be used in the present invention, bothfor the basic microchannel structure, and optionally for electronavalanche means as will be described below. In an MCP, a tubularcladding glass is mechanically supported in its bore by the insertion ofa rod of etchable core glass to produce a potential microchannel. Theassembly is then pulled through an oven and drawn down in diameter toproduce a microchannel (after the core is etched away). A plurality ofsuch drawn-down assemblies then are stacked and drawn down through theoven until a selected diameter is achieved for the core. Thereafter, theassembly is fused together and the cores are etched away leaving themicrochannel structure. While commercially available MCP's typically mayhave channels or capillaries ranging from about 5_m and 25_m indiameter, for photodetection purposes, it can be seen that any suitablediameter of channels can be fabricated by the above methods. Anothermanner of fabricating the microchannel structure of the presentinvention is to use conventional semi-conductor processing methods tocreate both the microchannels in an insulator material and the electrodelayer arrangements as will be described below.

In FIG. 12, an enlarged sectional view of a very small portion of themicrochannel structure shows several microchannels with open distalterminations 222 a-222 d in the working surface 215. In any embodiment,an electrode arrangement or layer indicated at 225 (also called theablation electrode) is provided with exposed surfaces 227 a-227 d thatinterface with volumes of media m₂ (a gas described in detail below)contained within the microchannels to thereafter apply energy to tissue.In this exemplary embodiment, a microchannel at its open end has across-section that is less than about 500 μm. More preferably, themicrochannels or chambers portions have a selected cross-sectionaldimension at the open terminations 222 a-222 d in that ranges from about5 μm to 400 μm (see FIG. 13). Still more preferably, the microchannelopen terminations 222 a-222 d range from about 25 μm to 200 μm. The openterminations are spaced apart by an insulator portion 224 ranging indimension from about 5 μm to 500 μm. In any Type “C” embodiment, theelectrode exposed surfaces 227 a-227 d are spaced inwardly or proximalfrom the distalmost working surface 215 a selected dimension d₂ thatranges from about 5 μm to 500 μm, in general varying in dimension indirect proportion with the cross-section of the channel and the voltagelevels used. In other words, the electrode exposed surfaces 227 a-227 dhave a covering layer of insulator material 224 that prevents directcontact of any electrode with tissue in contact with the surface 215.

In FIG. 12, an objective of the invention is illustrated wherein aparticular volume of media m₂ is shown captured in the distal portion oftwo channels 220 c and 220 d. The method of the invention creates thediscrete transient media volumes indicated at v, and thereafter ionizesand deionizes such volumes v, within microsecond intervals tocontrollably cause electrical energy to cross the media volume v from anelectrode exposed surface (e.g., 227 a-227 d) to the targeted site ts.In FIG. 12, the media volumes v are shaded to indicate an ionizedcondition as would occur when UV light is radiated through alight-channel 35 within member 212 exactly as described in the Type “A”embodiment (see FIG. 5C). For purposes of explaining the method of theinvention, FIG. 14A shows the media volume v independent of the workingend structure wherein the exterior boundary of the media volume v inherein termed a surface engagement plane sep wherein the media surfaceengages both the exposed electrode surface (e.g., 227 a-227 d) andtargeted tissue ts to deliver energy to tissue. FIG. 14B shows a singlemedia volume v in a perspective view of an end portion of a microchannel220 c. In FIGS. 14A-14B and subsequent Figures, the media volume v isillustrated with a proximal surface portion (with hatched graphics) thatis in contact with the electrode surfaces (e.g., 227 a-227 d of FIG. 12)herein called an electrode engagement area indicated at ee. In thisdisclosure and other applications cross-referenced herein, the conceptof controllably forming a volume v or bubble of media m₂ between anelectrode surface and a precisely localized target site ts is a keycomponent of the method of the invention. FIG. 12 shows the targetedsite ts as a grid of arbitrary units, for example at the smallest scalefrom about 5 μm to 10 μm, in which the volume v engages or contacts thetargeted site ts at a precise location to thereafter cause anenergy-tissue interaction eti proximate to the microchannel opentermination 222 a-222 d that will approximate the cross-sectionaldimension of that microchannel termination.

As can be seen in FIGS. 11-12, two other paired electrode layers 235 and245 are provided having electrode exposed surfaces 237 a-237 d and 247a-247 d within the microchannels, respectively. This electrode pair, andmore particularly electrode 245, is spaced apart from electrode layer225 by a suitable thickness insulator layer 224 to prevent thepossibility of unwanted electrical interactions between electrode layers225 and 245. The electrode pair 235 and 245 cooperate with each other toperform an optional method of the invention that utilizes high voltagesdescribed below, and thus the distal electrode 245 is spaced a selecteddimension d₃ from the distal working surface 215 to prevent anelectrical discharge to the targeted site ts from electrode 245 (seeFIG. 13). The electrode layers 235 and 245 are spaced apart a selecteddimension indicated at d₄ for causing an intense electrical fieldbetween the electrodes that cooperate with an electron-emissive surfacecoating 252 in the microchannel interior further described below. Allelectrodes 225, 235 and 245 are coupled to the electrical source 60 byseparate leads. The use of electrodes 235 and 245 offer an optionalenhanced mode for applying energy delivery to the targeted site ts(described below). In a basic energy delivery modality, thephotoionization means and single electrode layer 225 can be utilized tocause precise volumetric tissue removal, which is similar to methodperformed by the Type “A” system in FIGS. 5A-5E above and is brieflydescribed next.

In a first operational mode of the working end 210, FIGS. 15A-15Egraphically depict the use of the instrument and its distal workingsurface 215 to volumetrically remove surface tissues by causing aplurality of discrete and spaced apart, micro-scale, precisely localizedenergy-tissue interactions eti or ablations. FIG. 15A-15B show aperspective view of view three adjacent media volumes v within theworking surface 215, microchannels 220 a-220 c and open terminationsmicrochannels 222 a-222 c in phantom view. The open terminations 222a-222 c are within a dimensional range r of the surface of the targetedsite ts which again is graphically illustrated in a grid measured inarbitrary units. Of interest, the range r is defined as a particulardimension that is achievable by the method of the invention for creatinga directed path or conductive path cp of electrical energy irradiationbeyond the working surface 215 to deliver energy to tissue. In otherwords, it is postulated that UV radiation through the microchannels 220a-220 c will illuminate a conductive path cp extending substantiallybeyond the working surface 215 and within media ml (the surroundingnon-conductive gas environment) to the targeted site ts. The substantialconfinement of this conductive path within surrounding media ml willexist for a very brief interval before its ionization degrades andblends with the surrounding gas media m₁. However, during the intervalin which the conductive path is substantially intact, the path cp willdirect electrical energy through the free space fs beyond the workingsurface to the targeted site ts. In this respect, the conductive path cpin combination with the timed delivery of electrical energy fromelectrode engagement region ee exhibits the key characteristics of laserbeams insofar as utilized for laser-tissue interactions. That is,controlled amounts of energy can be delivered through free space to aprecisely localized point on the targeted site ts. The method of theinvention has a limited free space range r of energy propagation, whencompared to a laser, but it is believed the invention will provide arange r that is from about 100 μm to 2000 μm for working surfaces withthe larger above-specified microchannel terminations 222 a-222 c.

Again referring to FIGS. 15A-15B, the first Figure depicts (i) a neutralgas media such as the environment (air or m₁) stabilized in and aboutthe working surface or preferably (ii) a selected biocompatible neutralmedia m₂ (e.g., CO₂, argon, etc.) flowing through the microchannels froma source as detailed in the Type “A” embodiment. At this point in time,or a slight time interval prior to the ionization step of FIG. 15B,electrical potential is created at the electrodes and engagement area ee(e.g., at a time T₀). Optionally, the electrical potential is initiatedcontemporaneously with the ionization step of FIG. 15B. FIG. 15B depictsthe next step of the invention wherein the media volumes v that extendfrom the electrode engagement area ee to the targeted site ts areionized (e.g., at a time T₁), which is indicated graphically by shadingand further indicated as media m₂ being altered to media m₂′. In thismode of operation, the media is ionized by photoionization means (firstenergy source) comprising UV radiation delivered to the proximal end ofthe microchannel structure, based on the same means described in theType “A” embodiment which need not be repeated. As can be seen in FIG.15B, each open microchannel termination 222 a-222 c is within range r ofthe targeted site and the ionized media m₂′ extends across any freespacefs to interface with the targeted site in an area substantiallyequivalent to the cross section of the open termination 222 a-222 c.

FIG. 15C shows a view very similar to FIG. 15B and depicts the range rof the conductive path cp within the surrounding non-conductive media mlthat will occur for a brief interval, as described above. FIG. 15Dgraphically represents a result of the ionization step of FIGS. 15B and15C wherein the now conductive media m₂′ of the volumes v instantlydelivers electrical energy across the volumes v from the electrodeengagement areas ee to regions of the targeted surface ts engaged by thevolumes v. The energy application is graphically depicted by waveforms wof the electric field or discharge in FIG. 15D.

Of particular interest, FIG. 15E next graphically depicts theenergy-tissue interactions eti that would occur practicallycontemporaneous with the energy application step of FIG. 15D. It can beseen that a series of discrete, precisely localized, time-controlledenergy-tissue interactions eti or ablations will be caused by the methodof the invention and result in ejecta e of water vapor and cell debris.The intense energy potential at the electrode interface ee with the gasvolume v is carried to the tissue surface to cause intense energydensities that ablate tissue by vaporization of thin surface layers forthe brief interval that the ionized media m₂′ remains.

The next step of the method of the invention (not shown) is (i) thetermination of photoionizing UV radiation to the gas media in themicrochannel structure thereby returning such gases to a non-conductivenature (see FIG. 15A); and optionally (ii) the continuous or pulsedinflows of the neutral gas through the microchannel structure to insurethe gas volumes therein are instantly returned to neutral.Contemporaneous with this step, the electrical potential at theelectrodes is terminated.

Following the above sequence of steps which occur in a micro-second timeframe, the steps of the method are repeated after a very brief selectedinterval that exceeds the thermal relaxation of the targeted site, asdescribed above. The time intervals for utilizing the photoionizationmeans for switching the gas media from non-conductive to conductive maybe repeated at a pulse rate between about 200 ns and 500 ms. Statedanother way, the interval between repetitions of the complete steps ofphotoionization and electrical energy applications, may range from about500 ns to 500 ms to insure thermal relaxation of the targeted site.

It can be seen in FIG. 15E that energy application to a targeted site tswill result in a very even distribution of energy across the site havingthe dimensions of the width wf and length If of the working surface 215(see FIG. 11). Further, it can be understood that by painting theworking surface 215 across the targeted site ts, an even ablation willoccur in a path due to the large number of discrete energy-tissueinteraction sites eti (see FIG. 15E). In an early section of thisdisclosure, it was explained that in prior art ablation modalities, thedistribution of energy densities and ablation effects across an energyapplication site were random, and the dimensions across any such energyapplication site also would be random due to the random size of theinsulative bubble that is formed (see application of energy to tissue inFIG. 3) The working surface 215 and method of the present invention thussolve the problem of uneven and random energy distributions across atargeted site by the novel micronization means of the invention, withrespect both to the feature dimensions of the working surface 215 andthe resultant dimensions across a particular the energy-tissueinteraction eti. By this means, an aggregation or grid of such discretelocalized energy-tissue interactions eti (ablations) can be designed tocomprise any desired dimension of an ablation area, for example to matchthe size of a prior art ablation if desired. Further, the presentinvention thus can be favorably compared to a laser energy-tissueinteraction. In laser irradiation of a tissue surface, energydistribution across a site may be controlled largely by optics, with adesirable “top hat” energy distribution shown in FIG. 16A where energyis delivered evenly across an irradiated site, and the generally lesspreferred Gaussian energy distribution of FIG. 16B where higher energydensities are caused in the center of the site with a bell curvedefining a taper-off of the energy delivered toward the perimeter of thesite. Thus, the present invention, by distributing a large number ofdiscrete energy-tissue interactions evenly over a particular applicationof energy per selected time interval at a targeted site ts, it can besaid for the first time that energy can be applied to a targeted bodystructure from an electrical source that effectively results in asubstantially even “top hat” energy distribution across the site. It isbelieved that working electrode surfaces with features micronized asdescribed above to perform the novel method of electrosurgical ablationcan be used advantageously in every form of electrosurgical instrumentused for ablation, for example, simple mono-polar cutting electrodes,ablation catheter working ends, stereotactic needle working ends usedfor precise tumor ablation in the brain or breast or elsewhere, and allother ablation electrodes. The micronization of the energy tissueinteractions eti also limit collateral thermal damage to the level ofinsignificance due to the limited depth of any application of energythat is substantially confined within very thin surface cell layers.

The working end 215 of the device of FIGS. 10-11 may further be providedwith a perimeter suction channel as is known in the art (not shown) foraspirating tissue debris from the targeted site at the working end istranslated over the tissue. The open apertures or apertures of such asuction channel preferably would be spaced around the perimeter or edgeof the microchannel structure.

B. Alternative Energetic Plasma Mode of Operation of Type “C” WorkingEnd

The previous section described the application of high intensityelectrical energy in pulses to a targeted site ts to cause volumetricmaterial removal wherein the ablation will cause substantially littlecollateral thermal damage to tissue due to (i) the micron dimension ofthe discrete energy-tissue interactions that ablate only very thin celllayers, and (ii) the thermal relaxation of the targeted site ts betweentimed applications of energy at the 100's or 1000's of discrete,localized sites. It is believed that an alternative mode of operationwill prove possible with the Type “C” working end in which electricalenergy is delivered continuously to the microchannel structure, alongwith optional means of enhancing such energy delivery, to causesustainable highly energetic microplasma volumes about the openmicrochannel terminations 222 a-222 c (see FIG. 12) capable ofvolatilizing surface molecules over a selected time interval to causevolumetric material removal.

More in particular, referring to FIG. 17, the electron avalanche meansof the microchannel plate (MCP) structure may be energized in thisalternative mode of operation to create the energetic microplasmaindicated at m₂″ (i.e., m₂′identified ionized media in the previous modeof operation; m₂″ identifies the enhanced plasma of the alternativemode) about the exemplary open microchannel termination 222 a. The stepsof this alternative method comprise initially delivering appropriateelectrical energy to the paired electrode layers 235 and 245 of themicrochannel structure, which is in the range of 100 to 2000 volts.Thereafter, the steps previously described are initiated; that iselectrical potential is created at electrode 225 and then the UV sourceis triggered to photoionize the media volume v that is within themicrochannel structure. In this case, as depicted in FIG. 17, the UVphotons strike the electron-emissive surface coating 252 of themicrochannels between the paired electrode layers 235 and 245 and causean electron spray (avalanche) indicated at es wherein the electrons canfreely travel the minimal distance d₅ to greatly increase in the freeelectron population of the microplasma m₂″ to assist in the molecularvolatilization of the surface of the targeted site (see FIG. 17). Inthis mode of operation, the electrical potential at electrode layer 225may be continuous rather than pulsed to maintain the microplasmas at ahigh intensity, and if the dimension between the open microchannelterminations 222 a-222 b is small, it is believed that an energeticplasma volume will extend in a layer substantially across and about theworking surface 215 to interface with the targeted site ts. Thisinstrument and method, it is believed, will be able to create andsustain a sufficiently energetic microplasma to cause a trueplasma-mediated ablation of tissue at voltages at electrode 225 in therange of 100 V to 600 V. At these sufficiently high energy levels (orvoltage V), it is believed that energy in the range of 3.0 eV to 8.0 eVcan be created to cause breakdown of the carbon-carbon bonds,carbon-nitrogen bonds, and other similar bonds in surface molecules.When comparing the system disclosed by Eggers et al (U.S. Pat. Nos.5,873,855; 5,888,198; 5,891,095; 6,024,733; 6,032,674; 6,066,134) andcommercialized as the Coblator™ system, it can be easily understood thisprior art system expends much of its available energy to continuouslythermally vaporize random elements (NaCl) within a cool liquid toproduce random insulative gas bubbles over and about a large workingend, which bubbles thereafter are ionized randomly by an intenseelectrical discharge therein and there across. In contrast, the presentinvention expends no energy to vaporize a liquid to produce the requiredgas volumes. The present invention independently produces and introducesa neutral gas into the working end. Further, the present inventionutilizes both photoionization means and an optional electron avalanchemeans to energize the plasma volumes. Still further, the microplasmavolumes are captured within the microchannel structure and suchmicron-sized volumes can efficiently sustain an energetic plasma.

FIG. 18 illustrates a variation on the Type “C” working end of FIG. 17that provides a multiple layer MCP structure, in an optional chevronconfiguration, to further enhance the electron population of themicroplasmas m₂″. The working surface 215 again carries the sameelectrode 225. A first microchannel plate (MCP) layer (not-to-scale)indicated at 260 a has paired electrode layers 235 a and 245 a thatfunction as previously described. A second MCP layer (not-toscale)indicated at 260 b has paired electrode layers 235 b and 245 b. Theremay be further layers, and the purpose of the chevron pattern is causethe electron spray es from a more proximal layer to strike the walls ofthe more distal microchannel at an angle to thereby increase electronemissions.

C. Alternative Field Ionization (FI) Mode of Operation of Type “C”Working End

The previous sections have described the method of using a Type “C”working end wherein the ionization means comprise a light-carryingchannel 35 and a UV source to deliver energy to the working end. Otherionization means independent of the ablation electrode 225 are possiblehave been disclosed (see, e.g., co-pending U.S. Ser. No. 09/317,768filed May 24, 1999 (Docket No. S-QP-002) titled Photoionized Gas EnabledElectrical Discharge Technique for Plasma-Mediated Cold Tissue Ablation)and are listed again in the first paragraph of Section V above. Theremay be requirements for certain instruments that make it difficult orexpensive to rely on light-channeling means 35 to deliver UV energy to aworking surface. For example, it may be difficult to fabricate a lightchannel in an elongate catheter having a very small diameter. Also, itmay be expensive to fabricate a light channel in an elongate introducermember in which the axis of the microchannel structure is transverse tothe axis of the introducer.

For this reason, a working surface 215 with microchannel structuresubstantially the same as depicted in FIG. 12 may be used withoutphotoionization means. Instead, the paired electrode layers 235 and 245with exposed surfaces 237 and 247 within microchannels 220 a-220 d(absent electron-emissive coating 252) may be used to cause fieldionization of an introduced neutral gas, with the other steps of pulsedenergy delivery to cause tissue ablation the same as describedpreviously (see FIG. 19D).

Referring to FIGS. 19A-19C, an exemplary elongate catheter-type device280 is shown that is dimensioned for introduction through a workingchannel 282 of a gastroscope 283 for the thin layer ablation ofirregular or pre-cancerous cell layers in the mucosal lining mu of anesophagus, such as in a treatment of Barrett's esophagus (see FIG. 19A).It should be appreciated that the working end could be used for skinresurfacing or any other thin layer ablation. For example, thecatheter-type device 280 may be from about 2.0 mm. to 4.0 mm. indiameter. The working end 285 of the device is an insulator body 286 andcarries a microchannel structure having a distal working surface 215 andelectrode layer 225 substantially as described above (see FIGS.19B-19D). Referring to FIG. 19D, it can further be seen that themicrochannel structure carries paired, spaced apart electrode layers 235and 245, the same as in the previous configuration of FIG. 12 withoutelectron-emissive coating 252. The electrodes 235 and 245 are coupled tothe electrical source 60 by leads 287 a and 287 b, respectively (FIG.19B). The electrode layer 225 is coupled to the electrical source bylead 288. A simplified method of fabricating a microchannel structurefor experimentation as shown in FIG. 19C (or FIG. 12) is to sandwich twoMCP plates together as shown in more detail in FIG. 19D. The electrodelayers 235 and 245 of the more proximal plate are coupled to theelectrical source. Only the inner electrode 225 of the distal MCP iscoupled to the electrical source thus providing an electrode layerinsulated and spaced apart from the working surface.

In performing the method of the invention with the microchannelstructure of FIGS. 19A-19C, the neutral gas media m₂ flows through theinterior passageway 244 of the catheter body 268, as described in theprevious embodiment. As can be understood in FIG. 19C, the flow of mediam₂ through the microchannel structure displaces any surface fluidsindicated at m₁ from the mucosa. Next, the neutral media m₂ is alteredto a conductive or ionized media m₂′ by generating an intense electricfield within the microchannel portions between the paired electrodelayers 235 and 245 as depicted in FIG. 19D. In other words, fieldionization means are utilized to ionize the gas volumes flowing withinthe microchannel structure. The ionized gas will thereafter remainconductive as it flows through the working surface 215 thus creating theconductive media volumes v, the same as depicted in FIGS. 15C-15E. Theconductivity of the gas volumes v within and about the open microchannelterminations 222 a-222 z (cf. FIG. 15D) can thus be ionized anddeionized in rapid intervals (as described above with photoionization)by rapid on/off modulation of the intense electric field (e.g., rangingfrom 200 to 5000 volts) between paired electrode layers 235 and 245 toachieve pulsed energy applications and micro-scale ablations as depictedin FIG. 15E. It is believed that by providing an independent means(first energy source at electrodes 235 and 245) for switching the mediabetween conductive and non-conductive at a selected high repetitionrate, the invention will provide precise control over the briefintervals in which the energy-tissue interactions eti occur, rather thanthe uncontrolled intervals which would occur if high intensity currentwere delivered to electrode layer 225 alone to cause random timeintervals of ionization and electrical discharge across the gas volumes.As shown in FIG. 19A, the working end can be translated across themucosal lining mu under endoscopic vision to ablate very thin celllayers substantially without collateral thermal damage to deeper tissuelayers.

VI. Construction of Exemplary Type De “D” System for Plasma-AssistedMaterial Removal.

The previous sections described application of high intensity electricalenergy to cause volumetric removal of tissue layers (i) in a pulsed highintensity mode for creating micron dimensioned discrete energy-tissueinteractions to ablate tissue, or (ii) in the creation of a continuouslysustained layer of high energy microplasmas about the working surface ofthe instrument to cause true plasma-mediated molecular volatilization ofsurface macromolecules to remove tissue volume. The Type “D” systemdescribed next functions almost identically to plasma-mediated systemdescribed previously, with the exception that the electrode arrangementof the working surface is adapted to insure that maximal average voltageis applied to the ionized gas volumes v continuously (cf FIG. 15D),rather than in intervals that vary with current frequency.

A portion of the Type “D” working surface 315 and microchannel structureis shown in FIG. 20 with the novel electrode arrangement that comprisesat least two spaced apart electrode layers 325 a and 325 b instead ofone electrode layer (e.g., electrode layer 225 of the Type “C”embodiment of FIGS. 11-12). The scope of the invention includes anywherefrom 2 to about 4 electrode layers and for clarity, the invention isdescribed with two such electrode layers. FIG. 20 shows an exemplaryworking surface 315 and two electrode layers 325 a and 325 b withexposed surfaces 327 a and 327 b in the microchannels 320(collectively). These two electrode layers are separate from the MCPelectrode layers 235 and 245 that are the same as previously described.Each of the electrode layers 325 a and 325 b is coupled to theelectrical source 60 and controller 45 by a separate lead 329 a and 329b. Of particular interest, the electrical source 60 is capable ofgenerating overlapping waveforms of the voltage delivered to eachelectrode layer 325 a and 325 b, by which in meant that the energydelivered to each electrode's frequency is out of phase with the other,depicted as Phase A and Phase B in FIG. 20. In a system with two suchelectrode layers 325 a and 325 b, the phase of the waveforms would beshifted by about ½ the frequency of the waveform; in a system with threesuch electrode layers 325 a-325 c (not shown) the phase of the waveformswould be shifted by about ⅓ the frequency, etc. An electrical source 60can be adapted with circuitry known in the art to deliver suchout-of-phase voltage waveforms to the spaced apart electrodes.

In general, it is postulated that such a system with spaced apartelectrode layers 325 a and 325 b will cooperate with a return electrode85 to maintain high voltage energy delivery to microplasma volumes vformed about the open distal terminations 322 of microchannels to insurea continuous high energy plasma for causing molecular volatilization ofthe surface molecules at the targeted site ts. In the operation of theprevious Type “C” embodiment, the electric field between the electrode225 and return electrode 85 would diminish in intensity depending of thevoltage waveform as voltage difference between the active electrode 225and the return electrode 85 varied. In this embodiment, an additionalvoltage differential would occur at certain intervals of the selectedfrequency between the out-of-phase voltages at the electrode layers 325a and 325 b, in addition to the field created between these electrodelayers and the return electrode 85. Thus, a method of the inventionrelating to the Type “D” system comprises (i) providing at least twoclosely spaced electrodes that have overlapping or out-of-phase voltagewaveforms in an instrument working surface, in addition to a returnelectrode that cooperates with the working surface in contact with thetargeted site ts or on the spaced apart portion of the instrumentworking end, (ii) creating and transiently capturing (by any suitablebubble creation means) a neutral gas volume that engages the at leasttwo out-of-phase electrodes and further engages the targeted site ts;(iii) delivering intense energy to the electrode arrangement (e.g., infrequency range of about 250 kHz to 3.5 MHz) to sustainably ionized thetransient gas volumes at high energy levels sufficient to causevolumetric removal of the surface layers of the targeted site ts.

FIG. 21 generalizes the invention insofar as it relates to theutilization of multiple, closely spaced, overlapping phase electrodes325 a and 325 b in a multiple adjacent recessed channel or chamberportions 388 a-88 c having the above-described micron dimensions in aworking surface 390 that does not provide an independent means forintroducing neutral gas volumes to the working surface. In other words,the invention may be used with high-intensity energy delivery (describedabove) to vaporize insulative bubbles from a fluid on, or within, thetargeted tissue surface and to thereafter cause an intense energydischarge across the bubble to ablate tissue. The micron dimensions ofthe features of such a working surface 390 in combination with theout-of-phase energy applications to multiple electrodes provides a novelmodality of tissue ablation, wherein the intensity of energy deliveryacross the expanding and collapsing bubbles is enhanced by the higheraverage voltages over a selected time interval to cause limitedcollateral thermal damage.

VII. Construction of Exemplary Type “E” System for Energy Application

FIGS. 22A-22B below illustrate a Type “E” embodiment 400 that providesan additional energy delivery mode that has been found to optimize theformation, character and dimension of gas bubbles in the interfacebetween the working surface 415 and the targeted tissue.

More in particular, it has been found the application of vibrationalenergy to, and about, the working surface can increase the efficiency ofthe electrical energy application across the transient gas volume orbubbles that are formed between the working surface and the targetedtissue. In one embodiment, referring to FIG. 22, the instrument body 410extends to a working surface 415 that, for convenience shows a singlemedia entrance channel 422 but a plurality of microchannel entranceports are more practical for a typical dimension working end as shown inFIGS. 12, 13, 19C, 19C and 20. A remote source of a selected gas asdescribed previously is operatively coupled to the instrument to provideflow through the at least one single media entrance channel 422 to theworking surface.

The embodiment of FIG. 22A further shows that a vibration source 430 isoperatively coupled to the instrument body 410. The scope of theinvention includes any vibration source and preferably is any ultrasonictransducer known in the art that can couple acoustic energy to theinstrument body 410. One type of ultrasonic transmission system canprovide a proximal body portion (not shown) of the instrument (atransducer portion) that comprises at least one piezoelectric elementtogether with opposing polarity electrodes coupled to each such element.The piezoelectric elements can be fabricated of a suitable material,e.g., lead zirconate-titanate, or any other piezoelectric material. Inuse, the piezoelectric elements convert an electrical signal intomechanical energy that results in a longitudinal vibratory motion in ashaft portion of the instrument body to deliver such energy to theworking surface 415. Such an ultrasonic transmission unit is tunedacoustically as is known in the art to provide that the selectedlongitudinal vibration frequency that can be effective in vibrating thegas introduced through the at least one channel. In one embodiment, thegas is introduced through the working end surface through a plurality ofchannels having a cross-section of leas than about 1 micron. Morepreferably, the channels have a cross-section of less than about 0.5microns. State another way, the channels preferably are of a selecteddimension that is too small to allow inflow of fluid—but will stillallow gas flow therethrough. Such a dimension will insure that a gasvolume is trapped about the opening of each channel termination forenergy delivery thereacross.

When the above described ultrasonic assembly is energized, a vibratorymotion in the form of a standing wave is generated throughout the lengthof the instrument body 410. The propagation of such vibratory motion atparticular points along the length of the instrument body 410 depends onthe exact longitudinal location at which the vibratory motion ismeasured. A minimum in the vibratory motion or standing wave is commonlyreferred to as a node, wherein motion is at minimal level. The locationat which the vibratory motion reaches a peak in the standing wave isreferred to as an anti-node, and the length of the instrument body 410is selected to provide an anti-node characteristics generally at theworking surface 415 to deliver a maximum amount of energy thereto. Anysuitable electrical source and controller can be coupled to thepiezoelectric elements to drive or excite the ultrasonic assembly at anysuitable resonant frequency of the tuned acoustic assembly.

In operation, the piezoelectric elements are energized in response to anelectrical signal provided by source to thereby produce an acousticstanding wave in the instrument body contemporaneous with theintroduction of a selected gas to the working surface (see FIG.22A-22B). The delivery of the acoustic energy alters the characteristicof the gas volume transiently captured between the working surface andthe targeted tissue. The acoustic energy application has been found tobe useful for lowering the power or voltage requirements to applyablative energy across the gas interface between working surface 415 andthe targeted tissue, for example in the fluid environment of FIGS.22A-22B. Without wishing to be limited to any particular theory toexplain the reasons for the increases effectiveness of the energyapplication, it is believed that the acoustic energy alters ordiminishes the surface tension of the gas volume(s) or bubbles in thefluid environment, fragments the gas bubble(s) into smaller dimensions,detaches the gas bubbles from the working surface, or in general, veryrapidly creates a more refined gas volume between the working surfaceand the targeted tissue. By this means, the voltage required to cause anablative electrical discharge across the introduced gas is lessened.

The vibrational or acoustic energy as described above can be applied ina continuous manner to the working end, or it can be applied in a pulsedmanner. The scope of the invention includes the use of such vibrationalenergy in any electrosurgical working end that is adapted to applyenergy to tissue, and in particular to such instruments that are adaptedto apply energy for purposes of ablation or volumetric removal asdescribed above. The types of instrument working ends that fall withinthe scope of the invention includes, but is not limited to, probeworking ends for applying energy to tissue in procedures in orthopedics,endovascular interventions, neurointerventions, ENT, urology and generalsurgery. The invention also may be used in the jaws of grasping-typeinstruments. The vibrational energy can be combined with the instrumentsdescribed above that use photoionization of the gas volume, or thevibrational energy can be used independently thereof—still incombination with the electrical energy application components describedabove.

In another embodiment shown in FIG. 23, the probe working end 500 canuse ultrasound energy at the working surface 515 to create cavitationbubbles to provide an interface between the working surface and thetargeted tissue. Such cavitation bubbles can causes by an intense energyapplication of energy to a targeted media. When absorption of energy bythe target media results in thermoelastic expansion of the target and arise in internal pressures within the target. The term stressconfinement refers to the process of causing an increase in pressurewithin a targeted media before the pressure can dissipate from thetarget at the speed of sound. When there exists a defined or freeboundary between the targeted media and different surrounding media—suchas a liquid or gas interface with the target—the target expands at itssurface and then snaps back. The expansion phase is positive pressure orstress and the snap-back is negative stress. When the negative stressexceeds the strength of target media, that media breaks, disintegratesor ejects a surface portion thereof For example, an intense energyapplication whether from an electrical source, laser source or acoustic(mechanical) source can induce from 100° to 1000° C. temperature risesin a targeted composition and thereby can cause transient pressures offrom 100-1000 atmospheres to explode the targeted composition. The sameprocess of energy deposition in a targeted media can cause the formationof a bipolar positive/negative stress wave that propagates intosurrounding media. If the surrounding media were a substantially solidmaterial, the stress wave causes a fracture or break in the materialcalled a spall plane. If the surrounding media were a liquid or a softtissue, the bi-polar positive/negative stress wave would createcavitation bubbles in the media. In a liquid such as water, whenabsorbing energy in an intense manner, even a slight 5° to 20° C.temperature rise within a nanosecond or microsecond energy applicationinterval can yield a ±10 atm (atmosphere) bipolar stress wave—and the−10 atm negative stress can cause cavitation in water. Thus, theinvention can use ultrasound energy as is known in the art to createsuch cavitation bubbles (either in a continuous mode or pulsed mode).

The scope of the invention includes the application of acoustic energyto create cavitation bubbles in a fluid media about the working surfaceof the probe. Thereafter, the invention includes the application ofelectrical energy across the environment of expanding and collapsingcavitation bubbles to ablate tissue. This type of probe does not need agas inflow source of the previous embodiments, since the acousticcavitation system provides the desired interface between the workingsurface 515 and the targeted tissue. This type of working end can beused with or without the photoionization method and apparatus describedin previous embodiments.

While the plasma-assisted energy delivery methods above have beendescribed in connection with several surgical procedures for volumetrictissue removal, such as skin resurfacing, the ablation of pre-cancerousor malignant cell layers and in spine surgery, it will be clear to thosehaving skill in the art that the system has operational characteristicsthat may be suitable for a wide range of volumetric tissue removalprocedures in, or on, structure of a patient's body. The system andmethod of the invention are suitable for other arthroscopic surgeries,including partial meniscectomies, synovectomies, chondroplasties, tendonand cartilage removals, and in general resurfacing and texturing ofcartilage, tendon and bone surfaces. In addition, in the ENT and GIfields, there are a variety of procedures that require volumetric tissueremoval either at a tissue surface or at the end of a probe insertedpercutaneously in treating nose and throat disorders, for example, softpalate volume reduction surgery, turbinate reduction surgery and jawbone surgery. These procedures require that the surgeon be provided withmeans to remove tissue in close proximity to delicate structures andnerves that cannot be damaged, which procedures lend themselves to themethods disclosed herein. In many fields, the selective removal ofmalignant tissue or other tumors may be accomplished by the presentinvention. For example, a form of stereotactic-directed probe may beused to ablate breast lesions. The method of the invention also may haveuse in interventional cardiology to remove vascular occlusions. Themethod of the invention also may be useful for drilling holes in tissuesuch as in TMR procedures (transmyocardial revascularization). Thematerial removal methods described above apply to all body structures,which include non-anatomic structures such as accretions, calculi andthe like.

Those skilled in the art will appreciate that the exemplary embodimentsand descriptions thereof are merely illustrative of the invention as awhole, and that variations in controlling the duration of intervals ofenergy delivery, in controlling the repetition rate, and in controllingthe voltage applied to create the interval of intense electric fieldsmay be made within the spirit and scope of the invention. Accordingly,the present invention is not limited to the specific embodimentsdescribed herein, but includes the features disclosed in the author'sco-pending applications listed in the Section above titled“CROSS-REFERENCE TO RELATED APPLICATIONS” and the invention is definedby the scope of the appended claims. Specific features of the inventionmay be shown in some figures and not in others, and this is forconvenience only and any feature may be combined with another inaccordance with the invention. While the principles of the inventionhave been made clear in the exemplary embodiments, it will be obvious tothose skilled in the art that modifications of the structure,arrangement, proportions, elements, and materials may be utilized in thepractice of the invention, and otherwise, which are particularly adaptedto specific environments and operative requirements without departingfrom the principles of the invention. The appended claims are intendedto cover and embrace any and all such modifications, with the limitsonly of the true purview, spirit and scope of the invention.

1. A medical device for delivering energy to targeted tissue, comprising: an elongated member having a distal working end; an interior flow channel having a first cross-section, the flow channel transitioning to at least one channel portion having a second smaller cross-section and terminating in at least one outlet in the distal working end; at least one electrode element carried in said working end; and a conductive flow media source for providing a flow through the interior flow channel, and wherein the electrical energy delivery to the flow proximate the at last one outlet creates a plasma for ablation of tissue.
 2. The medical device of claim 1 further comprising a vibration source coupled to the elongated member.
 3. The medical device of claim 1 further comprising a vibration source coupled to the working end.
 4. The medical device of claim 1 wherein the at least one channel portion comprises one substantially linear channel.
 5. The medical device of claim 1 wherein the at least one channel portion comprises a plurality of substantially linear channels.
 6. The medical device of claim 1 wherein the at least one channel portion comprises a microporous structure.
 7. The medical device of claim 1 wherein the working end is a ceramic.
 8. The medical device of claim 1 wherein the at least one channel portion has a mean cross section across a principal axis of less than about 1000 microns.
 9. The medical device of claim 1 wherein the at least one channel portion has a mean cross section across a principal axis of less than about 500 microns.
 10. The medical device of claim 1 wherein the at least one channel portion has a mean cross section across a principal axis of less than about 250 microns.
 11. The medical device of claim 1 wherein the flow media comprises saline solution.
 12. The medical device of claim 1 wherein the flow media comprises hypertonic saline solution.
 13. The medical device of claim 1 further including first and second polarity electrical terminals for coupled electrical energy to the flow media.
 14. The medical device of claim 13 wherein the first polarity electrical terminal is within the interior channel.
 15. The medical device of claim 13 wherein the first polarity electrical terminal is within the on an exterior of the working end. 